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NAME

       erlang - The Erlang BIFs

DESCRIPTION

       By  convention,  most  built-in functions (BIFs) are seen as being in the module erlang. A
       number of the BIFs are viewed more or less as part of the Erlang programming language  and
       are auto-imported. Thus, it is not necessary to specify the module name and both the calls
       atom_to_list(Erlang) and erlang:atom_to_list(Erlang) are identical.

       In the text, auto-imported BIFs are listed without module prefix. BIFs listed with  module
       prefix are not auto-imported.

       BIFs  may  fail  for  a  variety  of reasons. All BIFs fail with reason badarg if they are
       called with arguments of an incorrect type. The other reasons that may make BIFs fail  are
       described in connection with the description of each individual BIF.

       Some BIFs may be used in guard tests, these are marked with "Allowed in guard tests".

DATA TYPES

       ext_binary()

              A binary data object, structured according to the Erlang external term format.

       timestamp() =
           {MegaSecs :: integer() >= 0,
            Secs :: integer() >= 0,
            MicroSecs :: integer() >= 0}

              See now/0.

EXPORTS

       abs(Float) -> float()

       abs(Int) -> integer() >= 0

              Types:

                 Float = float()
                 Int = integer()

              Returns  an  integer  or float which is the arithmetical absolute value of Float or
              Int.

              > abs(-3.33).
              3.33
              > abs(-3).
              3

              Allowed in guard tests.

       erlang:adler32(Data) -> integer() >= 0

              Types:

                 Data = iodata()

              Computes and returns the adler32 checksum for Data.

       erlang:adler32(OldAdler, Data) -> integer() >= 0

              Types:

                 OldAdler = integer() >= 0
                 Data = iodata()

              Continue computing  the  adler32  checksum  by  combining  the  previous  checksum,
              OldAdler, with the checksum of Data.

              The following code:

                   X = erlang:adler32(Data1),
                   Y = erlang:adler32(X,Data2).

              - would assign the same value to Y as this would:

                   Y = erlang:adler32([Data1,Data2]).

       erlang:adler32_combine(FirstAdler, SecondAdler, SecondSize) ->
                                 integer() >= 0

              Types:

                 FirstAdler = SecondAdler = SecondSize = integer() >= 0

              Combines  two  previously computed adler32 checksums. This computation requires the
              size of the data object for the second checksum to be known.

              The following code:

                   Y = erlang:adler32(Data1),
                   Z = erlang:adler32(Y,Data2).

              - would assign the same value to Z as this would:

                   X = erlang:adler32(Data1),
                   Y = erlang:adler32(Data2),
                   Z = erlang:adler32_combine(X,Y,iolist_size(Data2)).

       erlang:append_element(Tuple1, Term) -> Tuple2

              Types:

                 Tuple1 = Tuple2 = tuple()
                 Term = term()

              Returns a new tuple which has one  element  more  than  Tuple1,  and  contains  the
              elements in Tuple1 followed by Term as the last element. Semantically equivalent to
              list_to_tuple(tuple_to_list(Tuple1) ++ [Term]), but much faster.

              > erlang:append_element({one, two}, three).
              {one,two,three}

       apply(Fun, Args) -> term()

              Types:

                 Fun = function()
                 Args = [term()]

              Call a fun, passing the elements in Args as arguments.

              Note: If the number of elements in the arguments are  known  at  compile-time,  the
              call is better written as Fun(Arg1, Arg2, ... ArgN).

          Warning:
              Earlier, Fun could also be given as {Module, Function}, equivalent to apply(Module,
              Function, Args). This usage is deprecated and will stop working in a future release
              of Erlang/OTP.

       apply(Module, Function, Args) -> term()

              Types:

                 Module = module()
                 Function = atom()
                 Args = [term()]

              Returns  the  result  of  applying Function in Module to Args. The applied function
              must be exported from Module. The arity of the function is the length of Args.

              > apply(lists, reverse, [[a, b, c]]).
              [c,b,a]

              apply can be used to evaluate BIFs by using the module name erlang.

              > apply(erlang, atom_to_list, ['Erlang']).
              "Erlang"

              Note: If the number of arguments are known at  compile-time,  the  call  is  better
              written as Module:Function(Arg1, Arg2, ..., ArgN).

              Failure:  error_handler:undefined_function/3  is  called if the applied function is
              not exported. The error handler can  be  redefined  (see  process_flag/2).  If  the
              error_handler  is undefined, or if the user has redefined the default error_handler
              so the replacement  module  is  undefined,  an  error  with  the  reason  undef  is
              generated.

       atom_to_binary(Atom, Encoding) -> binary()

              Types:

                 Atom = atom()
                 Encoding = latin1 | unicode | utf8

              Returns  a binary which corresponds to the text representation of Atom. If Encoding
              is latin1, there will be one byte for each character in the text representation. If
              Encoding  is  utf8  or unicode, the characters will be encoded using UTF-8 (meaning
              that characters from 16#80 up to 0xFF will be encoded in two bytes).

          Note:
              Currently,  atom_to_binary(Atom,  latin1)  can  never   fail   because   the   text
              representation  of an atom can only contain characters from 0 to 16#FF. In a future
              release, the text representation of atoms might be allowed to contain  any  Unicode
              character and atom_to_binary(Atom, latin1) will fail if the text representation for
              the Atom contains a Unicode character greater than 16#FF.

              > atom_to_binary('Erlang', latin1).
              <<"Erlang">>

       atom_to_list(Atom) -> string()

              Types:

                 Atom = atom()

              Returns a string which corresponds to the text representation of Atom.

              > atom_to_list('Erlang').
              "Erlang"

       binary_part(Subject, PosLen) -> binary()

              Types:

                 Subject = binary()
                 PosLen = {Start :: integer() >= 0, Length :: integer()}

              Extracts the part of the binary described by PosLen.

              Negative length can be used to extract bytes at the end of a binary:

              1> Bin = <<1,2,3,4,5,6,7,8,9,10>>.
              2> binary_part(Bin,{byte_size(Bin), -5}).
              <<6,7,8,9,10>>

              If PosLen in any way references outside the binary, a badarg exception is raised.

              Start is zero-based, i.e.:

              1> Bin = <<1,2,3>>
              2> binary_part(Bin,{0,2}).
              <<1,2>>

              See the STDLIB module binary for details about the PosLen semantics.

              Allowed in guard tests.

       binary_part(Subject, Start, Length) -> binary()

              Types:

                 Subject = binary()
                 Start = integer() >= 0
                 Length = integer()

              The same as binary_part(Subject, {Start, Length}).

              Allowed in guard tests.

       binary_to_atom(Binary, Encoding) -> atom()

              Types:

                 Binary = binary()
                 Encoding = latin1 | unicode | utf8

              Returns the atom whose text representation is Binary. If  Encoding  is  latin1,  no
              translation  of  bytes  in  the binary is done. If Encoding is utf8 or unicode, the
              binary must contain valid UTF-8 sequences; furthermore, only Unicode characters  up
              to 0xFF are allowed.

          Note:
              binary_to_atom(Binary,  utf8)  will  fail if the binary contains Unicode characters
              greater than 16#FF. In a future release, such Unicode characters might  be  allowed
              and  binary_to_atom(Binary,  utf8) will not fail in that case. For more information
              on Unicode support in atoms see note on UTF-8 encoded atoms in  the  chapter  about
              the external term format in the ERTS User's Guide.

              > binary_to_atom(<<"Erlang">>, latin1).
              'Erlang'
              > binary_to_atom(<<1024/utf8>>, utf8).
              ** exception error: bad argument
                   in function  binary_to_atom/2
                      called as binary_to_atom(<<208,128>>,utf8)

       binary_to_existing_atom(Binary, Encoding) -> atom()

              Types:

                 Binary = binary()
                 Encoding = latin1 | unicode | utf8

              Works like binary_to_atom/2, but the atom must already exist.

              Failure: badarg if the atom does not already exist.

       binary_to_float(Binary) -> float()

              Types:

                 Binary = binary()

              Returns the float whose text representation is Binary.

              > binary_to_float(<<"2.2017764e+0">>).
              2.2017764

              Failure: badarg if Binary contains a bad representation of a float.

       binary_to_integer(Binary) -> integer()

              Types:

                 Binary = binary()

              Returns an integer whose text representation is Binary.

              > binary_to_integer(<<"123">>).
              123

              Failure: badarg if Binary contains a bad representation of an integer.

       binary_to_integer(Binary, Base) -> integer()

              Types:

                 Binary = binary()
                 Base = 2..36

              Returns an integer whose text representation in base Base is Binary.

              > binary_to_integer(<<"3FF">>, 16).
              1023

              Failure: badarg if Binary contains a bad representation of an integer.

       binary_to_list(Binary) -> [byte()]

              Types:

                 Binary = binary()

              Returns a list of integers which correspond to the bytes of Binary.

       binary_to_list(Binary, Start, Stop) -> [byte()]

              Types:

                 Binary = binary()
                 Start = Stop = integer() >= 1
                   1..byte_size(Binary)

              As binary_to_list/1, but returns a list of integers corresponding to the bytes from
              position Start to position Stop in Binary. Positions in  the  binary  are  numbered
              starting from 1.

          Note:
              This  function's  indexing  style  of  using  one-based  indices  for  binaries  is
              deprecated. New code should use the functions in the STDLIB module binary  instead.
              They consequently use the same (zero-based) style of indexing.

       bitstring_to_list(Bitstring) -> [byte() | bitstring()]

              Types:

                 Bitstring = bitstring()

              Returns  a  list  of  integers  which  correspond to the bytes of Bitstring. If the
              number of bits in the binary is not divisible by 8, the last element  of  the  list
              will be a bitstring containing the remaining bits (1 up to 7 bits).

       binary_to_term(Binary) -> term()

              Types:

                 Binary = ext_binary()

              Returns  an  Erlang  term which is the result of decoding the binary object Binary,
              which must be encoded according to the Erlang external term format.

          Warning:
              When decoding binaries from untrusted sources, consider using  binary_to_term/2  to
              prevent denial of service attacks.

              See also term_to_binary/1 and binary_to_term/2.

       binary_to_term(Binary, Opts) -> term()

              Types:

                 Binary = ext_binary()
                 Opts = [safe]

              As binary_to_term/1, but takes options that affect decoding of the binary.

                safe:
                  Use this option when receiving binaries from an untrusted source.

                  When  enabled,  it prevents decoding data that may be used to attack the Erlang
                  system. In the event of receiving unsafe data, decoding  fails  with  a  badarg
                  error.

                  Currently,  this prevents creation of new atoms directly, creation of new atoms
                  indirectly (as they are embedded in certain structures like pids,  refs,  funs,
                  etc.),  and  creation  of  new  external  function  references.  None  of those
                  resources are currently garbage collected, so unchecked creation  of  them  can
                  exhaust available memory.

              Failure: badarg if safe is specified and unsafe data is decoded.

              See also term_to_binary/1, binary_to_term/1, and  list_to_existing_atom/1.

       bit_size(Bitstring) -> integer() >= 0

              Types:

                 Bitstring = bitstring()

              Returns an integer which is the size in bits of Bitstring.

              > bit_size(<<433:16,3:3>>).
              19
              > bit_size(<<1,2,3>>).
              24

              Allowed in guard tests.

       erlang:bump_reductions(Reductions) -> true

              Types:

                 Reductions = integer() >= 1

              This  implementation-dependent  function  increments  the reduction counter for the
              calling  process.  In  the  Beam  emulator,  the  reduction  counter  is   normally
              incremented  by  one for each function and BIF call, and a context switch is forced
              when the counter reaches the maximum number  of  reductions  for  a  process  (2000
              reductions in R12B).

          Warning:
              This  BIF  might  be  removed in a future version of the Beam machine without prior
              warning. It is unlikely to be implemented in other Erlang implementations.

       byte_size(Bitstring) -> integer() >= 0

              Types:

                 Bitstring = bitstring()

              Returns an integer which is the number of bytes needed to contain Bitstring.  (That
              is,  if the number of bits in Bitstring is not divisible by 8, the resulting number
              of bytes will be rounded up.)

              > byte_size(<<433:16,3:3>>).
              3
              > byte_size(<<1,2,3>>).
              3

              Allowed in guard tests.

       erlang:cancel_timer(TimerRef) -> Time | false

              Types:

                 TimerRef = reference()
                 Time = integer() >= 0

              Cancels a timer, where TimerRef  was  returned  by  either  erlang:send_after/3  or
              erlang:start_timer/3. If the timer is there to be removed, the function returns the
              time in milliseconds left until the  timer  would  have  expired,  otherwise  false
              (which  means  that TimerRef was never a timer, that it has already been cancelled,
              or that it has already delivered its message).

              See also erlang:send_after/3, erlang:start_timer/3, and erlang:read_timer/1.

              Note: Cancelling a timer does not guarantee that the message has not  already  been
              delivered to the message queue.

       check_old_code(Module) -> boolean()

              Types:

                 Module = module()

              Returns true if the Module has old code, and false otherwise.

              See also code(3erl).

       check_process_code(Pid, Module) -> boolean()

              Types:

                 Pid = pid()
                 Module = module()

              Returns  true  if the process Pid is executing old code for Module. That is, if the
              current call of the process executes old code for this module, or  if  the  process
              has  references  to  old code for this module, or if the process contains funs that
              references old code for this module. Otherwise, it returns false.

              > check_process_code(Pid, lists).
              false

              See also code(3erl).

       erlang:crc32(Data) -> integer() >= 0

              Types:

                 Data = iodata()

              Computes and returns the crc32 (IEEE 802.3 style) checksum for Data.

       erlang:crc32(OldCrc, Data) -> integer() >= 0

              Types:

                 OldCrc = integer() >= 0
                 Data = iodata()

              Continue computing the crc32 checksum by combining the previous  checksum,  OldCrc,
              with the checksum of Data.

              The following code:

                   X = erlang:crc32(Data1),
                   Y = erlang:crc32(X,Data2).

              - would assign the same value to Y as this would:

                   Y = erlang:crc32([Data1,Data2]).

       erlang:crc32_combine(FirstCrc, SecondCrc, SecondSize) ->
                               integer() >= 0

              Types:

                 FirstCrc = SecondCrc = SecondSize = integer() >= 0

              Combines  two  previously  computed  crc32 checksums. This computation requires the
              size of the data object for the second checksum to be known.

              The following code:

                   Y = erlang:crc32(Data1),
                   Z = erlang:crc32(Y,Data2).

              - would assign the same value to Z as this would:

                   X = erlang:crc32(Data1),
                   Y = erlang:crc32(Data2),
                   Z = erlang:crc32_combine(X,Y,iolist_size(Data2)).

       date() -> Date

              Types:

                 Date = calendar:date()

              Returns the current date as {Year, Month, Day}.

              The time zone and daylight saving time correction depend on the underlying OS.

              > date().
              {1995,2,19}

       erlang:decode_packet(Type, Bin, Options) ->
                               {ok, Packet, Rest} |
                               {more, Length} |
                               {error, Reason}

              Types:

                 Type = raw
                      | 0
                      | 1
                      | 2
                      | 4
                      | asn1
                      | cdr
                      | sunrm
                      | fcgi
                      | tpkt
                      | line
                      | http
                      | http_bin
                      | httph
                      | httph_bin
                 Bin = binary()
                 Options = [Opt]
                 Opt = {packet_size, integer() >= 0}
                     | {line_length, integer() >= 0}
                 Packet = binary() | HttpPacket
                 Rest = binary()
                 Length = integer() >= 0 | undefined
                 Reason = term()
                 HttpPacket = HttpRequest
                            | HttpResponse
                            | HttpHeader
                            | http_eoh
                            | HttpError
                 HttpRequest = {http_request, HttpMethod, HttpUri, HttpVersion}
                 HttpResponse =
                     {http_response, HttpVersion, integer(), HttpString}
                 HttpHeader =
                     {http_header,
                      integer(),
                      HttpField,
                      Reserved :: term(),
                      Value :: HttpString}
                 HttpError = {http_error, HttpString}
                 HttpMethod = 'OPTIONS'
                            | 'GET'
                            | 'HEAD'
                            | 'POST'
                            | 'PUT'
                            | 'DELETE'
                            | 'TRACE'
                            | HttpString
                 HttpUri = '*'
                         | {absoluteURI,
                            http | https,
                            Host :: HttpString,
                            Port :: inet:port_number() | undefined,
                            Path :: HttpString}
                         | {scheme, Scheme :: HttpString, HttpString}
                         | {abs_path, HttpString}
                         | HttpString
                 HttpVersion =
                     {Major :: integer() >= 0, Minor :: integer() >= 0}
                 HttpField = 'Cache-Control'
                           | 'Connection'
                           | 'Date'
                           | 'Pragma'
                           | 'Transfer-Encoding'
                           | 'Upgrade'
                           | 'Via'
                           | 'Accept'
                           | 'Accept-Charset'
                           | 'Accept-Encoding'
                           | 'Accept-Language'
                           | 'Authorization'
                           | 'From'
                           | 'Host'
                           | 'If-Modified-Since'
                           | 'If-Match'
                           | 'If-None-Match'
                           | 'If-Range'
                           | 'If-Unmodified-Since'
                           | 'Max-Forwards'
                           | 'Proxy-Authorization'
                           | 'Range'
                           | 'Referer'
                           | 'User-Agent'
                           | 'Age'
                           | 'Location'
                           | 'Proxy-Authenticate'
                           | 'Public'
                           | 'Retry-After'
                           | 'Server'
                           | 'Vary'
                           | 'Warning'
                           | 'Www-Authenticate'
                           | 'Allow'
                           | 'Content-Base'
                           | 'Content-Encoding'
                           | 'Content-Language'
                           | 'Content-Length'
                           | 'Content-Location'
                           | 'Content-Md5'
                           | 'Content-Range'
                           | 'Content-Type'
                           | 'Etag'
                           | 'Expires'
                           | 'Last-Modified'
                           | 'Accept-Ranges'
                           | 'Set-Cookie'
                           | 'Set-Cookie2'
                           | 'X-Forwarded-For'
                           | 'Cookie'
                           | 'Keep-Alive'
                           | 'Proxy-Connection'
                           | HttpString
                 HttpString = string() | binary()

              Decodes the binary Bin according to the packet protocol  specified  by  Type.  Very
              similar to the packet handling done by sockets with the option {packet,Type}.

              If  an entire packet is contained in Bin it is returned together with the remainder
              of the binary as {ok,Packet,Rest}.

              If Bin does not contain the entire packet, {more,Length}  is  returned.  Length  is
              either  the  expected  total size of the packet or undefined if the expected packet
              size is not known. decode_packet can then be called again with more data added.

              If the packet does not conform to the protocol format {error,Reason} is returned.

              The following values of Type are valid:

                raw | 0:
                  No packet handling is done. Entire binary is returned unless it is empty.

                1 | 2 | 4:
                  Packets consist of a header specifying the  number  of  bytes  in  the  packet,
                  followed by that number of bytes. The length of header can be one, two, or four
                  bytes; the order of the bytes is big-endian. The header will  be  stripped  off
                  when the packet is returned.

                line:
                  A  packet  is a line terminated with newline. The newline character is included
                  in the returned packet unless the line was truncated according  to  the  option
                  line_length.

                asn1 | cdr | sunrm | fcgi | tpkt:
                  The header is not stripped off.

                  The meanings of the packet types are as follows:

                  asn1 - ASN.1 BER:

                  sunrm - Sun's RPC encoding:

                  cdr - CORBA (GIOP 1.1):

                  fcgi - Fast CGI:

                  tpkt - TPKT format [RFC1006]:

                http | httph | http_bin | httph_bin:
                  The  Hypertext  Transfer  Protocol.  The  packets  are returned with the format
                  according to HttpPacket described above.  A  packet  is  either  a  request,  a
                  response,  a  header  or  an  end of header mark. Invalid lines are returned as
                  HttpError.

                  Recognized request methods and header fields are returned as atoms. Others  are
                  returned  as  strings. Strings of unrecognized header fields are formatted with
                  only capital letters first and after hyphen  characters  (like  "Sec-Websocket-
                  Key").

                  The  protocol  type  http  should  only  be  used  for  the  first  line when a
                  HttpRequest or a HttpResponse is expected. The following calls should use httph
                  to  get  HttpHeader's  until  http_eoh  is  returned  that marks the end of the
                  headers and the beginning of any following message body.

                  The variants  http_bin  and  httph_bin  will  return  strings  (HttpString)  as
                  binaries instead of lists.

              The following options are available:

                {packet_size, integer() >= 0}:
                  Sets  the  max  allowed size of the packet body. If the packet header indicates
                  that the length of the packet is longer than the max allowed length, the packet
                  is considered invalid. Default is 0 which means no size limit.

                {line_length, integer() >= 0}:
                  For packet type line, truncate lines longer than the indicated length.

                  Option  line_length  also  applies to http* packet types as an alias for option
                  packet_size in the case when packet_size itself is not set. This usage is  only
                  intended for backward compatibility.

              > erlang:decode_packet(1,<<3,"abcd">>,[]).
              {ok,<<"abc">>,<<"d">>}
              > erlang:decode_packet(1,<<5,"abcd">>,[]).
              {more,6}

       erlang:delete_element(Index, Tuple1) -> Tuple2

              Types:

                 Index = integer() >= 1
                   1..tuple_size(Tuple1)
                 Tuple1 = Tuple2 = tuple()

              Returns a new tuple with element at Index removed from tuple Tuple1.

              > erlang:delete_element(2, {one, two, three}).
              {one,three}

       delete_module(Module) -> true | undefined

              Types:

                 Module = module()

              Makes  the  current code for Module become old code, and deletes all references for
              this module from the export table. Returns undefined if the module does not  exist,
              otherwise true.

          Warning:
              This  BIF  is  intended for the code server (see code(3erl)) and should not be used
              elsewhere.

              Failure: badarg if there is already an old version of Module.

       demonitor(MonitorRef) -> true

              Types:

                 MonitorRef = reference()

              If MonitorRef is  a  reference  which  the  calling  process  obtained  by  calling
              monitor/2,  this monitoring is turned off. If the monitoring is already turned off,
              nothing happens.

              Once  demonitor(MonitorRef)  has  returned  it  is  guaranteed  that  no   {'DOWN',
              MonitorRef,  _,  _,  _}  message  due to the monitor will be placed in the caller's
              message queue in the future. A {'DOWN', MonitorRef, _, _,  _}  message  might  have
              been  placed in the caller's message queue prior to the call, though. Therefore, in
              most cases, it is advisable to remove such a 'DOWN' message from the message  queue
              after  monitoring  has  been  stopped.  demonitor(MonitorRef,  [flush]) can be used
              instead of demonitor(MonitorRef) if this cleanup is wanted.

          Note:
              Prior to OTP  release  R11B  (erts  version  5.5)  demonitor/1  behaved  completely
              asynchronous, i.e., the monitor was active until the "demonitor signal" reached the
              monitored entity. This had one undesirable effect, though.  You  could  never  know
              when you were guaranteed not to receive a DOWN message due to the monitor.

              Current  behavior  can  be viewed as two combined operations: asynchronously send a
              "demonitor signal" to the monitored entity and ignore any  future  results  of  the
              monitor.

              Failure:  It  is  an  error if MonitorRef refers to a monitoring started by another
              process. Not all such cases are cheap to check; if  checking  is  cheap,  the  call
              fails with badarg (for example if MonitorRef is a remote reference).

       demonitor(MonitorRef, OptionList) -> boolean()

              Types:

                 MonitorRef = reference()
                 OptionList = [Option]
                 Option = flush | info

              The returned value is true unless info is part of OptionList.

              demonitor(MonitorRef, []) is equivalent to demonitor(MonitorRef).

              Currently the following Options are valid:

                flush:
                  Remove  (one)  {_,  MonitorRef,  _,  _,  _}  message, if there is one, from the
                  caller's message queue after monitoring has been stopped.

                  Calling demonitor(MonitorRef, [flush]) is equivalent to the following, but more
                  efficient:

                    demonitor(MonitorRef),
                    receive
                        {_, MonitorRef, _, _, _} ->
                            true
                    after 0 ->
                            true
                    end

                info:
                  The returned value is one of the following:

                  true:
                    The monitor was found and removed. In this case no 'DOWN' message due to this
                    monitor have been nor will be placed in the message queue of the caller.

                  false:
                    The monitor was not found and could not be  removed.  This  probably  because
                    someone  already has placed a 'DOWN' message corresponding to this monitor in
                    the caller's message queue.

                  If the info option is combined with the flush option, false will be returned if
                  a flush was needed; otherwise, true.

          Note:
              More options may be added in the future.

              Failure: badarg if OptionList is not a list, or if Option is not a valid option, or
              the same failure as for demonitor/1

       disconnect_node(Node) -> boolean() | ignored

              Types:

                 Node = node()

              Forces the disconnection of a node. This will appear to the node  Node  as  if  the
              local   node   has  crashed.  This  BIF  is  mainly  used  in  the  Erlang  network
              authentication protocols. Returns true if disconnection succeeds, otherwise  false.
              If the local node is not alive, the function returns ignored.

       erlang:display(Term) -> true

              Types:

                 Term = term()

              Prints a text representation of Term on the standard output.

          Warning:
              This BIF is intended for debugging only.

       element(N, Tuple) -> term()

              Types:

                 N = integer() >= 1
                   1..tuple_size(Tuple)
                 Tuple = tuple()

              Returns the Nth element (numbering from 1) of Tuple.

              > element(2, {a, b, c}).
              b

              Allowed in guard tests.

       erase() -> [{Key, Val}]

              Types:

                 Key = Val = term()

              Returns the process dictionary and deletes it.

              > put(key1, {1, 2, 3}),
              put(key2, [a, b, c]),
              erase().
              [{key1,{1,2,3}},{key2,[a,b,c]}]

       erase(Key) -> Val | undefined

              Types:

                 Key = Val = term()

              Returns  the  value  Val  associated  with  Key  and  deletes  it  from the process
              dictionary. Returns undefined if no value is associated with Key.

              > put(key1, {merry, lambs, are, playing}),
              X = erase(key1),
              {X, erase(key1)}.
              {{merry,lambs,are,playing},undefined}

       error(Reason) -> no_return()

              Types:

                 Reason = term()

              Stops the execution of the calling process with the reason Reason, where Reason  is
              any  term. The actual exit reason will be {Reason, Where}, where Where is a list of
              the functions most recently called (the current function first).  Since  evaluating
              this function causes the process to terminate, it has no return value.

              > catch error(foobar).
              {'EXIT',{foobar,[{erl_eval,do_apply,5},
                               {erl_eval,expr,5},
                               {shell,exprs,6},
                               {shell,eval_exprs,6},
                               {shell,eval_loop,3}]}}

       error(Reason, Args) -> no_return()

              Types:

                 Reason = term()
                 Args = [term()]

              Stops  the execution of the calling process with the reason Reason, where Reason is
              any term. The actual exit reason will be {Reason, Where}, where Where is a list  of
              the  functions  most recently called (the current function first). Args is expected
              to be the list of arguments for the current function; in Beam it will  be  used  to
              provide  the  actual  arguments  for  the current function in the Where term. Since
              evaluating this function causes the process to terminate, it has no return value.

       exit(Reason) -> no_return()

              Types:

                 Reason = term()

              Stops the execution of the calling process  with  the  exit  reason  Reason,  where
              Reason is any term. Since evaluating this function causes the process to terminate,
              it has no return value.

              > exit(foobar).
              ** exception exit: foobar
              > catch exit(foobar).
              {'EXIT',foobar}

       exit(Pid, Reason) -> true

              Types:

                 Pid = pid() | port()
                 Reason = term()

              Sends an exit signal with exit reason Reason to the process or port  identified  by
              Pid.

              The following behavior apply if Reason is any term except normal or kill:

              If  Pid is not trapping exits, Pid itself will exit with exit reason Reason. If Pid
              is trapping exits, the exit signal is transformed into  a  message  {'EXIT',  From,
              Reason}  and  delivered to the message queue of Pid. From is the pid of the process
              which sent the exit signal. See also process_flag/2.

              If Reason is the atom normal, Pid will not exit. If it is trapping exits, the  exit
              signal  is  transformed  into a message {'EXIT', From, normal} and delivered to its
              message queue.

              If Reason is the atom kill, that is if exit(Pid, kill) is  called,  an  untrappable
              exit signal is sent to Pid which will unconditionally exit with exit reason killed.

       erlang:external_size(Term) -> integer() >= 0

              Types:

                 Term = term()

              Calculates, without doing the encoding, the maximum byte size for a term encoded in
              the Erlang external term format. The following condition applies always:

              > Size1 = byte_size(term_to_binary(Term)),
              > Size2 = erlang:external_size(Term),
              > true = Size1 =< Size2.
              true

              This is equivalent to a call to:

              erlang:external_size(Term, [])

       erlang:external_size(Term, Options) -> integer() >= 0

              Types:

                 Term = term()
                 Options = [{minor_version, Version :: integer() >= 0}]

              Calculates, without doing the encoding, the maximum byte size for a term encoded in
              the Erlang external term format. The following condition applies always:

              > Size1 = byte_size(term_to_binary(Term, Options)),
              > Size2 = erlang:external_size(Term, Options),
              > true = Size1 =< Size2.
              true

              The   option  {minor_version,  Version}  specifies  how  floats  are  encoded.  See
              term_to_binary/2 for a more detailed description.

       float(Number) -> float()

              Types:

                 Number = number()

              Returns a float by converting Number to a float.

              > float(55).
              55.0

              Allowed in guard tests.

          Note:
              Note that if used on the top-level in a guard, it will test whether the argument is
              a floating point number; for clarity, use is_float/1 instead.

              When  float/1  is  used  in an expression in a guard, such as 'float(A) == 4.0', it
              converts a number as described above.

       float_to_binary(Float) -> binary()

              Types:

                 Float = float()

              The same as float_to_binary(Float,[{scientific,20}]).

       float_to_binary(Float, Options) -> binary()

              Types:

                 Float = float()
                 Options = [Option]
                 Option = {decimals, Decimals :: 0..253}
                        | {scientific, Decimals :: 0..249}
                        | compact

              Returns a binary which corresponds to the text representation of Float using  fixed
              decimal point formatting. The Options behave in the same way as float_to_list/2.

              > float_to_binary(7.12, [{decimals, 4}]).
              <<"7.1200">>
              > float_to_binary(7.12, [{decimals, 4}, compact]).
              <<"7.12">>

       float_to_list(Float) -> string()

              Types:

                 Float = float()

              The same as float_to_list(Float,[{scientific,20}]).

       float_to_list(Float, Options) -> string()

              Types:

                 Float = float()
                 Options = [Option]
                 Option = {decimals, Decimals :: 0..253}
                        | {scientific, Decimals :: 0..249}
                        | compact

              Returns  a string which corresponds to the text representation of Float using fixed
              decimal point formatting. When decimals option is specified the returned value will
              contain  at  most  Decimals  number of digits past the decimal point. If the number
              doesn't fit in the internal static buffer of 256 bytes, the function throws badarg.
              When  compact  option  is  provided  the  trailing zeros at the end of the list are
              truncated (this option is only meaningful together with the decimals option).  When
              scientific  option  is  provided,  the  float  will  be  formatted using scientific
              notation with Decimals digits of precision. If Options is [] the  function  behaves
              like float_to_list/1.

              > float_to_list(7.12, [{decimals, 4}]).
              "7.1200"
              > float_to_list(7.12, [{decimals, 4}, compact]).
              "7.12"

       erlang:fun_info(Fun) -> [{Item, Info}]

              Types:

                 Fun = function()
                 Item = arity
                      | env
                      | index
                      | name
                      | module
                      | new_index
                      | new_uniq
                      | pid
                      | type
                      | uniq
                 Info = term()

              Returns  a  list containing information about the fun Fun. Each element of the list
              is a tuple. The order of the tuples is not defined, and more tuples may be added in
              a future release.

          Warning:
              This  BIF  is  mainly  intended for debugging, but it can occasionally be useful in
              library functions that might need to verify, for instance, the arity of a fun.

              There are two types of funs with slightly different semantics:

              A fun created by fun M:F/A is called an external fun. Calling it will  always  call
              the  function  F  with  arity A in the latest code for module M. Note that module M
              does not even need to be loaded when the fun fun M:F/A is created.

              All other funs are called local. When a local fun is called, the  same  version  of
              the  code  that created the fun will be called (even if newer version of the module
              has been loaded).

              The following elements will always be present  in  the  list  for  both  local  and
              external funs:

                {type, Type}:
                  Type is either local or external.

                {module, Module}:
                  Module (an atom) is the module name.

                  If Fun is a local fun, Module is the module in which the fun is defined.

                  If Fun is an external fun, Module is the module that the fun refers to.

                {name, Name}:
                  Name (an atom) is a function name.

                  If  Fun  is a local fun, Name is the name of the local function that implements
                  the fun. (This name was generated by the compiler, and  is  generally  only  of
                  informational  use.  As  it  is a local function, it is not possible to call it
                  directly.) If no code is currently loaded for the  fun,  []  will  be  returned
                  instead of an atom.

                  If  Fun  is an external fun, Name is the name of the exported function that the
                  fun refers to.

                {arity, Arity}:
                  Arity is the number of arguments that the fun should be called with.

                {env, Env}:
                  Env (a list) is the environment or free variables for the  fun.  (For  external
                  funs, the returned list is always empty.)

              The following elements will only be present in the list if Fun is local:

                {pid, Pid}:
                  Pid is the pid of the process that originally created the fun.

                {index, Index}:
                  Index (an integer) is an index into the module's fun table.

                {new_index, Index}:
                  Index (an integer) is an index into the module's fun table.

                {new_uniq, Uniq}:
                  Uniq  (a  binary)  is  a  unique  value for this fun. It is calculated from the
                  compiled code for the entire module.

                {uniq, Uniq}:
                  Uniq (an integer) is a unique value for this fun. Starting in the R15  release,
                  this integer is calculated from the compiled code for the entire module. Before
                  R15, this integer was based on only the body of the fun.

       erlang:fun_info(Fun, Item) -> {Item, Info}

              Types:

                 Fun = function()
                 Item = fun_info_item()
                 Info = term()
                 fun_info_item() = arity
                                 | env
                                 | index
                                 | name
                                 | module
                                 | new_index
                                 | new_uniq
                                 | pid
                                 | type
                                 | uniq

              Returns information about Fun as specified by Item, in the form {Item,Info}.

              For any fun, Item can be any of the atoms module, name, arity, env, or type.

              For a local fun, Item can also be any of  the  atoms  index,  new_index,  new_uniq,
              uniq,  and  pid. For an external fun, the value of any of these items is always the
              atom undefined.

              See erlang:fun_info/1.

       erlang:fun_to_list(Fun) -> string()

              Types:

                 Fun = function()

              Returns a string which corresponds to the text representation of Fun.

       erlang:function_exported(Module, Function, Arity) -> boolean()

              Types:

                 Module = module()
                 Function = atom()
                 Arity = arity()

              Returns true if the module Module is  loaded  and  contains  an  exported  function
              Function/Arity; otherwise false.

              Returns false for any BIF (functions implemented in C rather than in Erlang).

       garbage_collect() -> true

              Forces  an  immediate  garbage  collection  of the currently executing process. The
              function should not be used, unless it has  been  noticed  --  or  there  are  good
              reasons  to  suspect -- that the spontaneous garbage collection will occur too late
              or not at all. Improper use may seriously degrade system performance.

              Compatibility note: In versions of OTP prior to R7,  the  garbage  collection  took
              place  at the next context switch, not immediately. To force a context switch after
              a call to erlang:garbage_collect(), it was sufficient to make any function call.

       garbage_collect(Pid) -> boolean()

              Types:

                 Pid = pid()

              Works like erlang:garbage_collect() but on any process.  The  same  caveats  apply.
              Returns false if Pid refers to a dead process; true otherwise.

       get() -> [{Key, Val}]

              Types:

                 Key = Val = term()

              Returns the process dictionary as a list of {Key, Val} tuples.

              > put(key1, merry),
              put(key2, lambs),
              put(key3, {are, playing}),
              get().
              [{key1,merry},{key2,lambs},{key3,{are,playing}}]

       get(Key) -> Val | undefined

              Types:

                 Key = Val = term()

              Returns the value Valassociated with Key in the process dictionary, or undefined if
              Key does not exist.

              > put(key1, merry),
              put(key2, lambs),
              put({any, [valid, term]}, {are, playing}),
              get({any, [valid, term]}).
              {are,playing}

       erlang:get_cookie() -> Cookie | nocookie

              Types:

                 Cookie = atom()

              Returns the magic cookie of the local node, if the node  is  alive;  otherwise  the
              atom nocookie.

       get_keys(Val) -> [Key]

              Types:

                 Val = Key = term()

              Returns  a  list  of  keys  which  are associated with the value Val in the process
              dictionary.

              > put(mary, {1, 2}),
              put(had, {1, 2}),
              put(a, {1, 2}),
              put(little, {1, 2}),
              put(dog, {1, 3}),
              put(lamb, {1, 2}),
              get_keys({1, 2}).
              [mary,had,a,little,lamb]

       erlang:get_stacktrace() -> [stack_item()]

              Types:

                 stack_item() =
                     {Module :: module(),
                      Function :: atom(),
                      Arity :: arity() | (Args :: [term()]),
                      Location ::
                          [{file, Filename :: string()} |
                           {line, Line :: integer() >= 1}]}

              Get the call stack back-trace (stacktrace) of the last  exception  in  the  calling
              process  as  a  list of {Module,Function,Arity,Location} tuples. The Arity field in
              the first tuple may be the argument list of that function call instead of an  arity
              integer, depending on the exception.

              If  there  has  not been any exceptions in a process, the stacktrace is []. After a
              code change for the process, the stacktrace may also be reset to [].

              The stacktrace is the same data as the catch operator returns, for example:

              {'EXIT',{badarg,Stacktrace}} = catch abs(x)

              Location is a (possibly empty) list of two-tuples that may indicate the location in
              the  source  code  of the function. The first element is an atom that describes the
              type of information in the second element. Currently the following items may occur:

                file:
                  The second element of the tuple is a string (list of  characters)  representing
                  the filename of the source file of the function.

                line:
                  The  second  element  of  the tuple is the line number (an integer greater than
                  zero) in the source file where the  exception  occurred  or  the  function  was
                  called.

              See also erlang:error/1 and erlang:error/2.

       group_leader() -> pid()

              Returns the pid of the group leader for the process which evaluates the function.

              Every process is a member of some process group and all groups have a group leader.
              All IO from the group is channeled to the group  leader.  When  a  new  process  is
              spawned,  it  gets  the  same  group  leader as the spawning process. Initially, at
              system start-up, init is both its own group leader and  the  group  leader  of  all
              processes.

       group_leader(GroupLeader, Pid) -> true

              Types:

                 GroupLeader = Pid = pid()

              Sets  the  group  leader  of  Pid  to  GroupLeader.  Typically, this is used when a
              processes started from a certain shell should have another group leader than init.

              See also group_leader/0.

       halt() -> no_return()

              The same as halt(0, []).

              > halt().
              os_prompt%

       halt(Status) -> no_return()

              Types:

                 Status = integer() >= 0 | abort | string()

              The same as halt(Status, []).

              > halt(17).
              os_prompt% echo $?
              17
              os_prompt%

       halt(Status, Options) -> no_return()

              Types:

                 Status = integer() >= 0 | abort | string()
                 Options = [Option]
                 Option = {flush, boolean()}

              Status must be a non-negative integer, a string,  or  the  atom  abort.  Halts  the
              Erlang runtime system. Has no return value. Depending on Status:

                integer():
                  The  runtime  system  exits with the integer value Status as status code to the
                  calling environment (operating system).

                string():
                  An erlang crash dump is produced with Status as slogan, and  then  the  runtime
                  system exits with status code 1.

                abort:
                   The  runtime  system  aborts  producing a core dump, if that is enabled in the
                  operating system.

              Note that on many platforms, only the status  codes  0-255  are  supported  by  the
              operating system.

              For  integer  Status  the  Erlang  runtime system closes all ports and allows async
              threads to finish their operations before exiting. To exit  without  such  flushing
              use Option as {flush,false}.

              For  statuses  string()  and  abort the flush option is ignored and flushing is not
              done.

       erlang:hash(Term, Range) -> integer() >= 1

              Types:

                 Term = term()
                 Range = integer() >= 1

              Returns a hash value for Term within the  range  1..Range.  The  allowed  range  is
              1..2^27-1.

          Warning:
              This  BIF  is  deprecated  as the hash value may differ on different architectures.
              Also the hash values for integer terms larger than 2^27 as well as  large  binaries
              are  very poor. The BIF is retained for backward compatibility reasons (it may have
              been used to hash records into a file), but all new code should use one of the BIFs
              erlang:phash/2 or erlang:phash2/1,2 instead.

       hd(List) -> term()

              Types:

                 List = [term(), ...]

              Returns the head of List, that is, the first element.

              > hd([1,2,3,4,5]).
              1

              Allowed in guard tests.

              Failure: badarg if List is the empty list [].

       erlang:hibernate(Module, Function, Args) -> no_return()

              Types:

                 Module = module()
                 Function = atom()
                 Args = [term()]

              Puts  the  calling  process  into a wait state where its memory allocation has been
              reduced as much as possible, which is useful if the  process  does  not  expect  to
              receive any messages in the near future.

              The process will be awaken when a message is sent to it, and control will resume in
              Module:Function with the arguments given by  Args  with  the  call  stack  emptied,
              meaning   that  the  process  will  terminate  when  that  function  returns.  Thus
              erlang:hibernate/3 will never return to its caller.

              If the process has any message in its message queue, the  process  will  be  awaken
              immediately in the same way as described above.

              In more technical terms, what erlang:hibernate/3 does is the following. It discards
              the call stack for the process. Then it garbage collects  the  process.  After  the
              garbage  collection,  all  live  data  is  in one continuous heap. The heap is then
              shrunken to the exact same size as the live data which it holds (even if that  size
              is less than the minimum heap size for the process).

              If the size of the live data in the process is less than the minimum heap size, the
              first garbage collection occurring after the process has been  awaken  will  ensure
              that the heap size is changed to a size not smaller than the minimum heap size.

              Note  that  emptying the call stack means that any surrounding catch is removed and
              has to be re-inserted after hibernation. One  effect  of  this  is  that  processes
              started  using proc_lib (also indirectly, such as gen_server processes), should use
              proc_lib:hibernate/3 instead to ensure that the exception handler continues to work
              when the process wakes up.

       erlang:insert_element(Index, Tuple1, Term) -> Tuple2

              Types:

                 Index = integer() >= 1
                   1..tuple_size(Tuple1) + 1
                 Tuple1 = Tuple2 = tuple()
                 Term = term()

              Returns a new tuple with element Term insert at position Index in tuple Tuple1. All
              elements from position Index and upwards are subsequently pushed one step higher in
              the new tuple Tuple2.

              > erlang:insert_element(2, {one, two, three}, new).
              {one,new,two,three}

       integer_to_binary(Integer) -> binary()

              Types:

                 Integer = integer()

              Returns a binary which corresponds to the text representation of Integer.

              > integer_to_binary(77).
              <<"77">>

       integer_to_binary(Integer, Base) -> binary()

              Types:

                 Integer = integer()
                 Base = 2..36

              Returns  a  binary  which corresponds to the text representation of Integer in base
              Base.

              > integer_to_binary(1023, 16).
              <<"3FF">>

       integer_to_list(Integer) -> string()

              Types:

                 Integer = integer()

              Returns a string which corresponds to the text representation of Integer.

              > integer_to_list(77).
              "77"

       integer_to_list(Integer, Base) -> string()

              Types:

                 Integer = integer()
                 Base = 2..36

              Returns a string which corresponds to the text representation of  Integer  in  base
              Base.

              > integer_to_list(1023, 16).
              "3FF"

       iolist_to_binary(IoListOrBinary) -> binary()

              Types:

                 IoListOrBinary = iolist() | binary()

              Returns a binary which is made from the integers and binaries in IoListOrBinary.

              > Bin1 = <<1,2,3>>.
              <<1,2,3>>
              > Bin2 = <<4,5>>.
              <<4,5>>
              > Bin3 = <<6>>.
              <<6>>
              > iolist_to_binary([Bin1,1,[2,3,Bin2],4|Bin3]).
              <<1,2,3,1,2,3,4,5,4,6>>

       iolist_size(Item) -> integer() >= 0

              Types:

                 Item = iolist() | binary()

              Returns  an  integer  which  is  the  size in bytes of the binary that would be the
              result of iolist_to_binary(Item).

              > iolist_size([1,2|<<3,4>>]).
              4

       is_alive() -> boolean()

              Returns true if the local node is alive; that is, if the node  can  be  part  of  a
              distributed system. Otherwise, it returns false.

       is_atom(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is an atom; otherwise returns false.

              Allowed in guard tests.

       is_binary(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is a binary; otherwise returns false.

              A binary always contains a complete number of bytes.

              Allowed in guard tests.

       is_bitstring(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is a bitstring (including a binary); otherwise returns false.

              Allowed in guard tests.

       is_boolean(Term) -> boolean()

              Types:

                 Term = term()

              Returns  true  if  Term is either the atom true or the atom false (i.e. a boolean);
              otherwise returns false.

              Allowed in guard tests.

       erlang:is_builtin(Module, Function, Arity) -> boolean()

              Types:

                 Module = module()
                 Function = atom()
                 Arity = arity()

              Returns true if Module:Function/Arity is a BIF implemented in C; otherwise  returns
              false. This BIF is useful for builders of cross reference tools.

       is_float(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is a floating point number; otherwise returns false.

              Allowed in guard tests.

       is_function(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is a fun; otherwise returns false.

              Allowed in guard tests.

       is_function(Term, Arity) -> boolean()

              Types:

                 Term = term()
                 Arity = arity()

              Returns  true  if Term is a fun that can be applied with Arity number of arguments;
              otherwise returns false.

              Allowed in guard tests.

       is_integer(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is an integer; otherwise returns false.

              Allowed in guard tests.

       is_list(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is a list with zero or more elements; otherwise returns false.

              Allowed in guard tests.

       is_number(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is either an integer or a  floating  point  number;  otherwise
              returns false.

              Allowed in guard tests.

       is_pid(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is a pid (process identifier); otherwise returns false.

              Allowed in guard tests.

       is_port(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is a port identifier; otherwise returns false.

              Allowed in guard tests.

       is_process_alive(Pid) -> boolean()

              Types:

                 Pid = pid()

              Pid  must  refer to a process at the local node. Returns true if the process exists
              and is alive, that is, is not exiting and has not exited. Otherwise, returns false.

       is_record(Term, RecordTag) -> boolean()

              Types:

                 Term = term()
                 RecordTag = atom()

              Returns true if Term is a tuple and its  first  element  is  RecordTag.  Otherwise,
              returns false.

          Note:
              Normally  the  compiler  treats  calls  to  is_record/2 specially. It emits code to
              verify that Term is a tuple, that its first element is RecordTag, and that the size
              is  correct.  However,  if the RecordTag is not a literal atom, the is_record/2 BIF
              will be called instead and the size of the tuple will not be verified.

              Allowed in guard tests, if RecordTag is a literal atom.

       is_record(Term, RecordTag, Size) -> boolean()

              Types:

                 Term = term()
                 RecordTag = atom()
                 Size = integer() >= 0

              RecordTag must be an atom. Returns true if Term is a tuple, its  first  element  is
              RecordTag, and its size is Size. Otherwise, returns false.

              Allowed  in  guard  tests,  provided that RecordTag is a literal atom and Size is a
              literal integer.

          Note:
              This BIF is documented for completeness. In most cases is_record/2 should be used.

       is_reference(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is a reference; otherwise returns false.

              Allowed in guard tests.

       is_tuple(Term) -> boolean()

              Types:

                 Term = term()

              Returns true if Term is a tuple; otherwise returns false.

              Allowed in guard tests.

       length(List) -> integer() >= 0

              Types:

                 List = [term()]

              Returns the length of List.

              > length([1,2,3,4,5,6,7,8,9]).
              9

              Allowed in guard tests.

       link(PidOrPort) -> true

              Types:

                 PidOrPort = pid() | port()

              Creates a link between the calling process and another process (or port) PidOrPort,
              if  there  is  not  such  a link already. If a process attempts to create a link to
              itself, nothing is done. Returns true.

              If PidOrPort does not exist, the behavior of the BIF  depends  on  if  the  calling
              process is trapping exits or not (see process_flag/2):

                * If  the  calling process is not trapping exits, and checking PidOrPort is cheap
                  -- that is, if PidOrPort is local -- link/1 fails with reason noproc.

                * Otherwise, if the calling  process  is  trapping  exits,  and/or  PidOrPort  is
                  remote,  link/1  returns true, but an exit signal with reason noproc is sent to
                  the calling process.

       list_to_atom(String) -> atom()

              Types:

                 String = string()

              Returns the atom whose text representation is String.

              String may only contain ISO-latin-1 characters (i.e.  numbers  below  256)  as  the
              current  implementation does not allow unicode characters >= 256 in atoms. For more
              information on Unicode support in atoms see note on  UTF-8  encoded  atoms  in  the
              chapter about the external term format in the ERTS User's Guide.

              > list_to_atom("Erlang").
              'Erlang'

       list_to_binary(IoList) -> binary()

              Types:

                 IoList = iolist()

              Returns a binary which is made from the integers and binaries in IoList.

              > Bin1 = <<1,2,3>>.
              <<1,2,3>>
              > Bin2 = <<4,5>>.
              <<4,5>>
              > Bin3 = <<6>>.
              <<6>>
              > list_to_binary([Bin1,1,[2,3,Bin2],4|Bin3]).
              <<1,2,3,1,2,3,4,5,4,6>>

       list_to_bitstring(BitstringList) -> bitstring()

              Types:

                 BitstringList = bitstring_list()
                 bitstring_list() =
                     maybe_improper_list(byte() | bitstring() | bitstring_list(),
                                         bitstring() | [])

              Returns   a   bitstring   which  is  made  from  the  integers  and  bitstrings  in
              BitstringList. (The last tail in BitstringList is allowed to be a bitstring.)

              > Bin1 = <<1,2,3>>.
              <<1,2,3>>
              > Bin2 = <<4,5>>.
              <<4,5>>
              > Bin3 = <<6,7:4,>>.
              <<6>>
              > list_to_bitstring([Bin1,1,[2,3,Bin2],4|Bin3]).
              <<1,2,3,1,2,3,4,5,4,6,7:46>>

       list_to_existing_atom(String) -> atom()

              Types:

                 String = string()

              Returns the atom whose text representation is String, but  only  if  there  already
              exists such atom.

              Failure:  badarg  if there does not already exist an atom whose text representation
              is String.

       list_to_float(String) -> float()

              Types:

                 String = string()

              Returns the float whose text representation is String.

              > list_to_float("2.2017764e+0").
              2.2017764

              Failure: badarg if String contains a bad representation of a float.

       list_to_integer(String) -> integer()

              Types:

                 String = string()

              Returns an integer whose text representation is String.

              > list_to_integer("123").
              123

              Failure: badarg if String contains a bad representation of an integer.

       list_to_integer(String, Base) -> integer()

              Types:

                 String = string()
                 Base = 2..36

              Returns an integer whose text representation in base Base is String.

              > list_to_integer("3FF", 16).
              1023

              Failure: badarg if String contains a bad representation of an integer.

       list_to_pid(String) -> pid()

              Types:

                 String = string()

              Returns a pid whose text representation is String.

          Warning:
              This BIF is intended for debugging and for use in the Erlang operating  system.  It
              should not be used in application programs.

              > list_to_pid("<0.4.1>").
              <0.4.1>

              Failure: badarg if String contains a bad representation of a pid.

       list_to_tuple(List) -> tuple()

              Types:

                 List = [term()]

              Returns a tuple which corresponds to List. List can contain any Erlang terms.

              > list_to_tuple([share, ['Ericsson_B', 163]]).
              {share, ['Ericsson_B', 163]}

       load_module(Module, Binary) -> {module, Module} | {error, Reason}

              Types:

                 Module = module()
                 Binary = binary()
                 Reason = badfile | not_purged | on_load

              If  Binary  contains  the  object  code  for the module Module, this BIF loads that
              object code. Also, if the code for the module Module  already  exists,  all  export
              references  are  replaced  so  they  point to the newly loaded code. The previously
              loaded code is kept in the system as old code, as  there  may  still  be  processes
              which  are  executing  that  code.  It  returns either {module, Module}, or {error,
              Reason} if loading fails. Reason is one of the following:

                badfile:
                  The object code in Binary has an incorrect format or the object  code  contains
                  code for another module than Module.

                not_purged:
                  Binary  contains  a  module  which  cannot  be loaded because old code for this
                  module already exists.

          Warning:
              This BIF is intended for the code server (see code(3erl)) and should  not  be  used
              elsewhere.

       erlang:load_nif(Path, LoadInfo) -> ok | Error

              Types:

                 Path = string()
                 LoadInfo = term()
                 Error = {error, {Reason, Text :: string()}}
                 Reason = load_failed
                        | bad_lib
                        | load
                        | reload
                        | upgrade
                        | old_code

          Note:
              In releases older than OTP R14B, NIFs were an experimental feature. Versions of OTP
              older than R14B might have different and possibly incompatible  NIF  semantics  and
              interfaces.   For   example,   in   R13B03   the   return   value  on  failure  was
              {error,Reason,Text}.

              Loads and links a dynamic library containing native  implemented  functions  (NIFs)
              for a module. Path is a file path to the sharable object/dynamic library file minus
              the OS-dependent file extension (.so for Unix and .dll for Windows). See erl_nif on
              how to implement a NIF library.

              LoadInfo  can  be  any  term.  It  will  be passed on to the library as part of the
              initialization. A good practice is to include a module version  number  to  support
              future code upgrade scenarios.

              The  call  to  load_nif/2  must be made directly from the Erlang code of the module
              that the NIF library belongs to.

              It returns either ok, or {error,{Reason,Text}} if loading fails. Reason is  one  of
              the  atoms  below,  while  Text  is a human readable string that may give some more
              information about the failure.

                load_failed:
                  The OS failed to load the NIF library.

                bad_lib:
                  The library did not fulfil the requirements as a NIF  library  of  the  calling
                  module.

                load | reload | upgrade:
                  The corresponding library callback was not successful.

                old_code:
                  The  call  to  load_nif/2  was made from the old code of a module that has been
                  upgraded. This is not allowed.

       erlang:loaded() -> [Module]

              Types:

                 Module = module()

              Returns a list of all loaded Erlang modules (current and/or  old  code),  including
              preloaded modules.

              See also code(3erl).

       erlang:localtime() -> DateTime

              Types:

                 DateTime = calendar:datetime()

              Returns  the  current  local  date  and  time  {{Year,  Month, Day}, {Hour, Minute,
              Second}}.

              The time zone and daylight saving time correction depend on the underlying OS.

              > erlang:localtime().
              {{1996,11,6},{14,45,17}}

       erlang:localtime_to_universaltime(Localtime) -> Universaltime

              Types:

                 Localtime = Universaltime = calendar:datetime()

              Converts local date and time to  Universal  Time  Coordinated  (UTC),  if  this  is
              supported  by  the underlying OS. Otherwise, no conversion is done and Localtime is
              returned.

              > erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}).
              {{1996,11,6},{13,45,17}}

              Failure: badarg if Localtime does not denote a valid date and time.

       erlang:localtime_to_universaltime(Localtime, IsDst) ->
                                            Universaltime

              Types:

                 Localtime = Universaltime = calendar:datetime()
                 IsDst = true | false | undefined

              Converts local date  and  time  to  Universal  Time  Coordinated  (UTC)  just  like
              erlang:localtime_to_universaltime/1, but the caller decides if daylight saving time
              is active or not.

              If IsDst == true the Localtime is during daylight saving time, if IsDst == false it
              is not, and if IsDst == undefined the underlying OS may guess, which is the same as
              calling erlang:localtime_to_universaltime(Localtime).

              > erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, true).
              {{1996,11,6},{12,45,17}}
              > erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, false).
              {{1996,11,6},{13,45,17}}
              > erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, undefined).
              {{1996,11,6},{13,45,17}}

              Failure: badarg if Localtime does not denote a valid date and time.

       make_ref() -> reference()

              Returns an almost unique reference.

              The returned reference will re-occur after approximately 2^82 calls;  therefore  it
              is unique enough for practical purposes.

              > make_ref().
              #Ref<0.0.0.135>

       erlang:make_tuple(Arity, InitialValue) -> tuple()

              Types:

                 Arity = arity()
                 InitialValue = term()

              Returns a new tuple of the given Arity, where all elements are InitialValue.

              > erlang:make_tuple(4, []).
              {[],[],[],[]}

       erlang:make_tuple(Arity, DefaultValue, InitList) -> tuple()

              Types:

                 Arity = arity()
                 DefaultValue = term()
                 InitList = [{Position :: integer() >= 1, term()}]

              erlang:make_tuple  first  creates  a tuple of size Arity where each element has the
              value DefaultValue. It then fills in values from InitList.  Each  list  element  in
              InitList  must  be  a  two-tuple where the first element is a position in the newly
              created tuple and the second element is any term. If a position  occurs  more  than
              once in the list, the term corresponding to last occurrence will be used.

              > erlang:make_tuple(5, [], [{2,ignored},{5,zz},{2,aa}]).
              {{[],aa,[],[],zz}

       max(Term1, Term2) -> Maximum

              Types:

                 Term1 = Term2 = Maximum = term()

              Return  the  largest  of Term1 and Term2; if the terms compare equal, Term1 will be
              returned.

       erlang:md5(Data) -> Digest

              Types:

                 Data = iodata()
                 Digest = binary()

              Computes an MD5 message digest from Data, where the length of  the  digest  is  128
              bits (16 bytes). Data is a binary or a list of small integers and binaries.

              See The MD5 Message Digest Algorithm (RFC 1321) for more information about MD5.

          Warning:
              The  MD5  Message  Digest  Algorithm  is  not  considered  safe for code-signing or
              software integrity purposes.

       erlang:md5_final(Context) -> Digest

              Types:

                 Context = Digest = binary()

              Finishes the update of an MD5 Context and returns the computed MD5 message digest.

       erlang:md5_init() -> Context

              Types:

                 Context = binary()

              Creates an MD5 context, to be used in subsequent calls to md5_update/2.

       erlang:md5_update(Context, Data) -> NewContext

              Types:

                 Context = binary()
                 Data = iodata()
                 NewContext = binary()

              Updates an MD5 Context with Data, and returns a NewContext.

       erlang:memory() -> [{Type, Size}]

              Types:

                 Type = memory_type()
                 Size = integer() >= 0
                 memory_type() = total
                               | processes
                               | processes_used
                               | system
                               | atom
                               | atom_used
                               | binary
                               | code
                               | ets
                               | low
                               | maximum

              Returns a list containing information about memory  dynamically  allocated  by  the
              Erlang  emulator.  Each  element  of  the  list  is a tuple {Type, Size}. The first
              element Typeis an atom describing memory type. The  second  element  Sizeis  memory
              size in bytes. A description of each memory type follows:

                total:
                  The total amount of memory currently allocated, which is the same as the sum of
                  memory size for processes and system.

                processes:
                  The total amount of memory currently allocated by the Erlang processes.

                processes_used:
                  The total amount of memory currently used by the Erlang processes.

                  This memory is part of the memory presented as processes memory.

                system:
                  The total amount of memory currently allocated by  the  emulator  that  is  not
                  directly related to any Erlang process.

                  Memory presented as processes is not included in this memory.

                atom:
                  The total amount of memory currently allocated for atoms.

                  This memory is part of the memory presented as system memory.

                atom_used:
                  The total amount of memory currently used for atoms.

                  This memory is part of the memory presented as atom memory.

                binary:
                  The total amount of memory currently allocated for binaries.

                  This memory is part of the memory presented as system memory.

                code:
                  The total amount of memory currently allocated for Erlang code.

                  This memory is part of the memory presented as system memory.

                ets:
                  The total amount of memory currently allocated for ets tables.

                  This memory is part of the memory presented as system memory.

                low:
                  Only on 64-bit halfword emulator.

                  The total amount of memory allocated in low memory areas that are restricted to
                  less than 4 Gb even though the system may have more physical memory.

                  May be removed in future releases of halfword emulator.

                maximum:
                  The maximum total amount of memory allocated since the emulator was started.

                  This tuple is only present when the emulator is run with instrumentation.

                  For  information  on  how  to  run  the  emulator  with   instrumentation   see
                  instrument(3erl) and/or erl(1).

          Note:
              The  system value is not complete. Some allocated memory that should be part of the
              system value are not.

              When the emulator is run with instrumentation, the system value is  more  accurate,
              but  memory  directly  allocated  by malloc (and friends) are still not part of the
              system value. Direct calls to  malloc  are  only  done  from  OS  specific  runtime
              libraries  and  perhaps  from  user  implemented Erlang drivers that do not use the
              memory allocation functions in the driver interface.

              Since the total value is the sum of processes and system the error in  system  will
              propagate to the total value.

              The  different  amounts of memory that are summed are not gathered atomically which
              also introduce an error in the result.

              The different values has the following relation to  each  other.  Values  beginning
              with an uppercase letter is not part of the result.

                      total = processes + system
                      processes = processes_used + ProcessesNotUsed
                      system = atom + binary + code + ets + OtherSystem
                      atom = atom_used + AtomNotUsed

                      RealTotal = processes + RealSystem
                      RealSystem = system + MissedSystem

              More tuples in the returned list may be added in the future.

          Note:
              The  total value is supposed to be the total amount of memory dynamically allocated
              by the emulator. Shared libraries,  the  code  of  the  emulator  itself,  and  the
              emulator  stack(s) are not supposed to be included. That is, the total value is not
              supposed to be equal to the total  size  of  all  pages  mapped  to  the  emulator.
              Furthermore,  due to fragmentation and pre-reservation of memory areas, the size of
              the memory segments which contain the dynamically allocated memory  blocks  can  be
              substantially  larger  than  the  total  size  of  the dynamically allocated memory
              blocks.

          Note:
              Since  erts  version  5.6.4  erlang:memory/0  requires  that  all  erts_alloc(3erl)
              allocators are enabled (default behaviour).

              Failure:

                notsup:
                   If an erts_alloc(3erl) allocator has been disabled.

       erlang:memory(Type :: memory_type()) -> integer() >= 0

       erlang:memory(TypeList :: [memory_type()]) ->
                        [{memory_type(), integer() >= 0}]

              Types:

                 memory_type() = total
                               | processes
                               | processes_used
                               | system
                               | atom
                               | atom_used
                               | binary
                               | code
                               | ets
                               | low
                               | maximum

              Returns  the  memory  size in bytes allocated for memory of type Type. The argument
              can also be given as a list of memory_type() atoms, in which case  a  corresponding
              list of {memory_type(), Size :: integer >= 0} tuples is returned.

          Note:
              Since  erts  version  5.6.4  erlang:memory/1  requires  that  all  erts_alloc(3erl)
              allocators are enabled (default behaviour).

              Failures:

                badarg:
                   If Type is not one  of  the  memory  types  listed  in  the  documentation  of
                  erlang:memory/0.

                badarg:
                   If maximum is passed as Type and the emulator is not run in instrumented mode.

                notsup:
                   If an erts_alloc(3erl) allocator has been disabled.

              See also erlang:memory/0.

       min(Term1, Term2) -> Minimum

              Types:

                 Term1 = Term2 = Minimum = term()

              Return  the  smallest of Term1 and Term2; if the terms compare equal, Term1 will be
              returned.

       module_loaded(Module) -> boolean()

              Types:

                 Module = module()

              Returns true if the module Module is loaded, otherwise returns false. It  does  not
              attempt to load the module.

          Warning:
              This  BIF  is  intended for the code server (see code(3erl)) and should not be used
              elsewhere.

       monitor(Type, Item) -> MonitorRef

              Types:

                 Type = process
                 Item = pid() | RegName | {RegName, Node}
                 RegName = module()
                 Node = node()
                 MonitorRef = reference()

              The calling process starts monitoring Item which is an object of type Type.

              Currently only processes can be monitored, i.e. the only allowed Type  is  process,
              but other types may be allowed in the future.

              Item can be:

                pid():
                  The pid of the process to monitor.

                {RegName, Node}:
                  A  tuple  consisting  of  a  registered  name of a process and a node name. The
                  process residing on the node Node with the  registered  name  RegName  will  be
                  monitored.

                RegName:
                  The process locally registered as RegName will be monitored.

          Note:
              When a process is monitored by registered name, the process that has the registered
              name at the time when monitor/2 is called will be monitored. The monitor  will  not
              be effected, if the registered name is unregistered.

              A  'DOWN' message will be sent to the monitoring process if Item dies, if Item does
              not exist, or if the connection is lost to the node which Item resides on. A 'DOWN'
              message has the following pattern:

              {'DOWN', MonitorRef, Type, Object, Info}

              where MonitorRef and Type are the same as described above, and:

                Object:
                  A reference to the monitored object:

                  * the pid of the monitored process, if Item was specified as a pid.

                  * {RegName, Node}, if Item was specified as {RegName, Node}.

                  * {RegName,  Node}, if Item was specified as RegName. Node will in this case be
                    the name of the local node (node()).

                Info:
                  Either the exit reason  of  the  process,  noproc  (non-existing  process),  or
                  noconnection (no connection to Node).

          Note:
              If/when monitor/2 is extended (e.g. to handle other item types than process), other
              possible values for Object, and Info in the 'DOWN' message will be introduced.

              The monitoring is turned off either when  the  'DOWN'  message  is  sent,  or  when
              demonitor/1 is called.

              If  an  attempt is made to monitor a process on an older node (where remote process
              monitoring is not implemented or one where remote process monitoring by  registered
              name is not implemented), the call fails with badarg.

              Making  several calls to monitor/2 for the same Item is not an error; it results in
              as many, completely independent, monitorings.

          Note:
              The format of the 'DOWN' message changed in the 5.2 version of  the  emulator  (OTP
              release  R9B)  for  monitor  by  registered  name. The Object element of the 'DOWN'
              message could in earlier versions sometimes be the pid of the monitored process and
              sometimes  be  the  registered  name.  Now  the  Object  element  is always a tuple
              consisting of the registered name  and  the  node  name.  Processes  on  new  nodes
              (emulator version 5.2 or greater) will always get 'DOWN' messages on the new format
              even if they are monitoring processes on old nodes. Processes  on  old  nodes  will
              always get 'DOWN' messages on the old format.

       monitor_node(Node, Flag) -> true

              Types:

                 Node = node()
                 Flag = boolean()

              Monitors  the status of the node Node. If Flag is true, monitoring is turned on; if
              Flag is false, monitoring is turned off.

              Making several calls to monitor_node(Node, true) for the same Node is not an error;
              it results in as many, completely independent, monitorings.

              If  Node  fails or does not exist, the message {nodedown, Node} is delivered to the
              process. If a process has made two  calls  to  monitor_node(Node,  true)  and  Node
              terminates,  two  nodedown  messages  are  delivered to the process. If there is no
              connection to Node, there will be an attempt  to  create  one.  If  this  fails,  a
              nodedown message is delivered.

              Nodes connected through hidden connections can be monitored as any other node.

              Failure: badarg if the local node is not alive.

       erlang:monitor_node(Node, Flag, Options) -> true

              Types:

                 Node = node()
                 Flag = boolean()
                 Options = [Option]
                 Option = allow_passive_connect

              Behaves as monitor_node/2 except that it allows an extra option to be given, namely
              allow_passive_connect. The option allows the BIF to wait the normal net  connection
              timeout  for  the  monitored  node to connect itself, even if it cannot be actively
              connected from this node (i.e. it is blocked). The state where this might be useful
              can  only  be  achieved  by using the kernel option dist_auto_connect once. If that
              kernel option is not used, the allow_passive_connect option has no effect.

          Note:
              The allow_passive_connect option  is  used  internally  and  is  seldom  needed  in
              applications  where  the network topology and the kernel options in effect is known
              in advance.

              Failure: badarg if the local node is not alive or the option list is malformed.

       erlang:nif_error(Reason) -> no_return()

              Types:

                 Reason = term()

              Works exactly like erlang:error/1, but Dialyzer thinks that this BIF will return an
              arbitrary  term.  When  used  in a stub function for a NIF to generate an exception
              when the NIF library is not loaded, Dialyzer will not generate false warnings.

       erlang:nif_error(Reason, Args) -> no_return()

              Types:

                 Reason = term()
                 Args = [term()]

              Works exactly like erlang:error/2, but Dialyzer thinks that this BIF will return an
              arbitrary  term.  When  used  in a stub function for a NIF to generate an exception
              when the NIF library is not loaded, Dialyzer will not generate false warnings.

       node() -> Node

              Types:

                 Node = node()

              Returns the name of the local node. If the node  is  not  alive,  nonode@nohost  is
              returned instead.

              Allowed in guard tests.

       node(Arg) -> Node

              Types:

                 Arg = pid() | port() | reference()
                 Node = node()

              Returns the node where Arg is located. Arg can be a pid, a reference, or a port. If
              the local node is not alive, nonode@nohost is returned.

              Allowed in guard tests.

       nodes() -> Nodes

              Types:

                 Nodes = [node()]

              Returns a list of all visible nodes in the system, excluding the local  node.  Same
              as nodes(visible).

       nodes(Arg) -> Nodes

              Types:

                 Arg = NodeType | [NodeType]
                 NodeType = visible | hidden | connected | this | known
                 Nodes = [node()]

              Returns  a  list of nodes according to argument given. The result returned when the
              argument is a list, is the list of nodes satisfying the disjunction(s) of the  list
              elements.

              NodeType can be any of the following:

                visible:
                  Nodes connected to this node through normal connections.

                hidden:
                  Nodes connected to this node through hidden connections.

                connected:
                  All nodes connected to this node.

                this:
                  This node.

                known:
                  Nodes which are known to this node, i.e., connected, previously connected, etc.

              Some   equalities:  [node()]  =  nodes(this),  nodes(connected)  =  nodes([visible,
              hidden]), and nodes() = nodes(visible).

              If the local node is not alive, nodes(this) == nodes(known) == [nonode@nohost], for
              any other Arg the empty list [] is returned.

       now() -> Timestamp

              Types:

                 Timestamp = timestamp()
                 timestamp() =
                     {MegaSecs :: integer() >= 0,
                      Secs :: integer() >= 0,
                      MicroSecs :: integer() >= 0}

              Returns the tuple {MegaSecs, Secs, MicroSecs} which is the elapsed time since 00:00
              GMT, January 1, 1970 (zero hour) on the assumption that the underlying OS  supports
              this.  Otherwise,  some  other  point in time is chosen. It is also guaranteed that
              subsequent calls to this BIF returns continuously  increasing  values.  Hence,  the
              return  value  from  now() can be used to generate unique time-stamps, and if it is
              called in a tight loop on a fast machine the time of the node can become skewed.

              It can only be used to check the local time of day if the  time-zone  info  of  the
              underlying operating system is properly configured.

              If  you do not need the return value to be unique and monotonically increasing, use
              os:timestamp/0 instead to avoid some overhead.

       open_port(PortName, PortSettings) -> port()

              Types:

                 PortName = {spawn, Command :: string()}
                          | {spawn_driver, Command :: [byte()]}
                          | {spawn_executable, FileName :: file:name()}
                          | {fd,
                             In :: integer() >= 0,
                             Out :: integer() >= 0}
                 PortSettings = [Opt]
                 Opt = {packet, N :: 1 | 2 | 4}
                     | stream
                     | {line, L :: integer() >= 0}
                     | {cd, Dir :: string()}
                     | {env,
                        Env :: [{Name :: string(), Val :: string() | false}]}
                     | {args, [string() | binary()]}
                     | {arg0, string() | binary()}
                     | exit_status
                     | use_stdio
                     | nouse_stdio
                     | stderr_to_stdout
                     | in
                     | out
                     | binary
                     | eof
                     | {parallelism, Boolean :: boolean()}
                     | hide

              Returns a port identifier as the result of opening a new Erlang port. A port can be
              seen as an external Erlang process. PortName is one of the following:

                {spawn, Command}:
                  Starts  an  external program. Command is the name of the external program which
                  will be run. Command runs outside the Erlang work space unless an Erlang driver
                  with the name Command is found. If found, that driver will be started. A driver
                  runs in the Erlang workspace, which means that it is  linked  with  the  Erlang
                  runtime system.

                  When  starting  external  programs on Solaris, the system call vfork is used in
                  preference to fork for performance reasons, although it has a history of  being
                  less  robust.  If  there are problems with using vfork, setting the environment
                  variable ERL_NO_VFORK to any value will cause fork to be used instead.

                  For external programs, the PATH is searched (or an equivalent method is used to
                  find  programs,  depending  on  operating system). This is done by invoking the
                  shell on certain platforms. The first space separated token of the command will
                  be  considered  as  the  name  of the executable (or driver). This (among other
                  things) makes this option unsuitable for running programs having spaces in file
                  or  directory  names.  Use  {spawn_executable,  Command}  instead  if spaces in
                  executable file names is desired.

                {spawn_driver, Command}:
                  Works like {spawn, Command}, but demands the first (space separated)  token  of
                  the  command  to be the name of a loaded driver. If no driver with that name is
                  loaded, a badarg error is raised.

                {spawn_executable, FileName}:
                  Works like {spawn, FileName}, but only runs external executables. The  FileName
                  in  its  whole  is used as the name of the executable, including any spaces. If
                  arguments are to be passed, the args and arg0 PortSettings can be used.

                  The shell is not usually invoked to start the program, it's executed  directly.
                  Neither  is the PATH (or equivalent) searched. To find a program in the PATH to
                  execute, use os:find_executable/1.

                  Only if a shell script or  .bat  file  is  executed,  the  appropriate  command
                  interpreter  will  implicitly  be  invoked,  but there will still be no command
                  argument expansion or implicit PATH search.

                  The name of the executable as well as the arguments given in args and  arg0  is
                  subject  to  Unicode  file name translation if the system is running in Unicode
                  file name mode. To avoid translation or force i.e. UTF-8, supply the executable
                  and/or  arguments as a binary in the correct encoding. See the file module, the
                  file:native_name_encoding/0 function and the stdlib users guide  for details.

            Note:
                The characters in the name (if given as a list) can only be > 255 if  the  Erlang
                VM  is  started  in Unicode file name translation mode, otherwise the name of the
                executable is limited to the ISO-latin-1 character set.

                  If the FileName cannot be run, an error exception, with the posix error code as
                  the  reason,  is raised. The error reason may differ between operating systems.
                  Typically the error enoent is raised when one tries to run a  program  that  is
                  not found and eaccess is raised when the given file is not executable.

                {fd, In, Out}:
                  Allows  an  Erlang process to access any currently opened file descriptors used
                  by Erlang. The file descriptor In can be used for standard input, and the  file
                  descriptor  Out for standard output. It is only used for various servers in the
                  Erlang operating system (shell and user). Hence, its use is very limited.

              PortSettings is a list of settings for the port. Valid settings are:

                {packet, N}:
                  Messages are preceded  by  their  length,  sent  in  N  bytes,  with  the  most
                  significant byte first. Valid values for N are 1, 2, or 4.

                stream:
                  Output  messages  are sent without packet lengths. A user-defined protocol must
                  be used between the Erlang process and the external object.

                {line, L}:
                  Messages are delivered on a per line basis. Each line  (delimited  by  the  OS-
                  dependent  newline  sequence)  is  delivered in one single message. The message
                  data format is {Flag, Line}, where Flag is either eol or noeol and Line is  the
                  actual data delivered (without the newline sequence).

                  L  specifies  the  maximum line length in bytes. Lines longer than this will be
                  delivered in more than one message, with the Flag set to noeol for all but  the
                  last  message.  If  end  of  file is encountered anywhere else than immediately
                  following a newline sequence, the last line will also  be  delivered  with  the
                  Flag  set  to  noeol.  In all other cases, lines are delivered with Flag set to
                  eol.

                  The {packet, N} and {line, L} settings are mutually exclusive.

                {cd, Dir}:
                  This is only valid for {spawn, Command} and {spawn_executable,  FileName}.  The
                  external  program  starts  using  Dir  as  its working directory. Dir must be a
                  string.

                {env, Env}:
                  This is only valid for {spawn, Command} and {spawn_executable,  FileName}.  The
                  environment   of   the  started  process  is  extended  using  the  environment
                  specifications in Env.

                  Env should be a list of tuples {Name, Val},  where  Name  is  the  name  of  an
                  environment  variable,  and  Val is the value it is to have in the spawned port
                  process. Both Name and Val must be strings. The one exception is Val being  the
                  atom  false  (in  analogy  with  os:getenv/1),  which  removes  the environment
                  variable.

                  If Unicode filename encoding is in  effect  (see  the  erl  manual  page),  the
                  strings (both Name and Value) may contain characters with codepoints > 255.

                {args, [ string() | binary() ]}:
                  This  option  is  only  valid  for  {spawn_executable,  FileName} and specifies
                  arguments to the executable. Each argument is given as a  separate  string  and
                  (on  Unix)  eventually  ends  up as one element each in the argument vector. On
                  other platforms, similar behavior is mimicked.

                  The arguments are not expanded by the shell prior  to  being  supplied  to  the
                  executable,  most  notably  this  means  that  file wildcard expansion will not
                  happen. Use filelib:wildcard/1 to expand wildcards for the arguments. Note that
                  even  if  the  program  is  a  Unix  shell  script, meaning that the shell will
                  ultimately be invoked, wildcard expansion will not happen and the  script  will
                  be  provided with the untouched arguments. On Windows(R), wildcard expansion is
                  always up to the program itself, why this isn't an issue.

                  Note also that the actual executable name (a.k.a. argv[0]) should not be  given
                  in  this list. The proper executable name will automatically be used as argv[0]
                  where applicable.

                  When the Erlang VM is running in Unicode file  name  mode,  the  arguments  can
                  contain  any  Unicode  characters  and  will  be  translated  into  whatever is
                  appropriate on the underlying OS, which means UTF-8 for  all  platforms  except
                  Windows,  which  has  other  (more  transparent)  ways  of dealing with Unicode
                  arguments to programs. To avoid Unicode translation of arguments, they  can  be
                  supplied as binaries in whatever encoding is deemed appropriate.

            Note:
                The  characters in the arguments (if given as a list of characters) can only be >
                255 if the Erlang VM  is  started  in  Unicode  file  name  mode,  otherwise  the
                arguments are limited to the ISO-latin-1 character set.

                  If  one,  for  any  reason,  wants  to  explicitly  set the program name in the
                  argument vector, the arg0 option can be used.

                {arg0, string() | binary()}:
                  This option is only  valid  for  {spawn_executable,  FileName}  and  explicitly
                  specifies  the  program name argument when running an executable. This might in
                  some circumstances, on some operating systems, be desirable.  How  the  program
                  responds  to  this  is  highly  system  dependent  and  no  specific  effect is
                  guaranteed.

                  The unicode file name translation rules of the args option apply to this option
                  as well.

                exit_status:
                  This  is  only  valid  for {spawn, Command} where Command refers to an external
                  program, and for {spawn_executable, FileName}.

                  When the external process connected to the port exits, a message  of  the  form
                  {Port,{exit_status,Status}}  is  sent to the connected process, where Status is
                  the exit status of the external process. If the program  aborts,  on  Unix  the
                  same convention is used as the shells do (i.e., 128+signal).

                  If  the  eof option has been given as well, the eof message and the exit_status
                  message appear in an unspecified order.

                  If the port program closes its stdout without exiting, the  exit_status  option
                  will not work.

                use_stdio:
                  This  is  only  valid for {spawn, Command} and {spawn_executable, FileName}. It
                  allows the standard input and output (file descriptors 0 and 1) of the  spawned
                  (UNIX) process for communication with Erlang.

                nouse_stdio:
                  The opposite of use_stdio. Uses file descriptors 3 and 4 for communication with
                  Erlang.

                stderr_to_stdout:
                  Affects ports to external programs. The  executed  program  gets  its  standard
                  error  file  redirected  to  its  standard  output  file.  stderr_to_stdout and
                  nouse_stdio are mutually exclusive.

                overlapped_io:
                  Affects ports to external programs on Windows(R) only. The standard  input  and
                  standard  output  handles of the port program will, if this option is supplied,
                  be opened with the flag FILE_FLAG_OVERLAPPED, so that the port program can (and
                  has  to)  do  overlapped  I/O on its standard handles. This is not normally the
                  case for simple port programs, but an  option  of  value  for  the  experienced
                  Windows programmer. On all other platforms, this option is silently discarded.

                in:
                  The port can only be used for input.

                out:
                  The port can only be used for output.

                binary:
                  All IO from the port are binary data objects as opposed to lists of bytes.

                eof:
                  The  port will not be closed at the end of the file and produce an exit signal.
                  Instead, it will remain open and a {Port, eof} message  will  be  sent  to  the
                  process holding the port.

                hide:
                  When  running  on  Windows,  suppress  creation  of  a  new console window when
                  spawning the port program. (This option has no effect on other platforms.)

                {parallelism, Boolean}:
                  Set scheduler hint for port parallelism. If set to true, the VM  will  schedule
                  port tasks when it by this can improve the parallelism in the system. If set to
                  false, the VM will try to perform port tasks immediately and by this  improving
                  the  latency  at  the  expense of parallelism. The default can be set on system
                  startup by passing the +spp command line argument to erl(1).

              The default is stream for all types of port and use_stdio for spawned ports.

              Failure: If the port cannot be opened, the exit reason is badarg, system_limit,  or
              the  Posix error code which most closely describes the error, or einval if no Posix
              code is appropriate:

                badarg:
                  Bad input arguments to open_port.

                system_limit:
                  All available ports in the Erlang emulator are in use.

                enomem:
                  There was not enough memory to create the port.

                eagain:
                  There are no more available operating system processes.

                enametoolong:
                  The external command given was too long.

                emfile:
                  There are no more available file descriptors (for the operating system  process
                  that the Erlang emulator runs in).

                enfile:
                  The file table is full (for the entire operating system).

                eacces:
                  The  Command  given  in  {spawn_executable,  Command}  does  not  point  out an
                  executable file.

                enoent:
                  The FileName given in  {spawn_executable,  FileName}  does  not  point  out  an
                  existing file.

              During  use  of  a  port  opened  using  {spawn,  Name},  {spawn_driver,  Name}  or
              {spawn_executable, Name}, errors arising when sending messages to it  are  reported
              to  the  owning  process  using  signals of the form {'EXIT', Port, PosixCode}. See
              file(3erl) for possible values of PosixCode.

              The maximum number of ports that can be open at the same time can be configured  by
              passing the +Q command line flag to erl(1).

       erlang:phash(Term, Range) -> Hash

              Types:

                 Term = term()
                 Range = Hash = integer() >= 1
                   Range = 1..2^32, Hash = 1..Range

              Portable  hash  function  that  will  give  the  same hash for the same Erlang term
              regardless of machine architecture and ERTS version (the BIF was introduced in ERTS
              4.9.1.1).  Range  can  be between 1 and 2^32, the function returns a hash value for
              Term within the range 1..Range.

              This BIF could be used instead of the  old  deprecated  erlang:hash/2  BIF,  as  it
              calculates better hashes for all data-types, but consider using phash2/1,2 instead.

       erlang:phash2(Term) -> Hash

       erlang:phash2(Term, Range) -> Hash

              Types:

                 Term = term()
                 Range = integer() >= 1
                   1..2^32
                 Hash = integer() >= 0
                   0..Range-1

              Portable  hash  function  that  will  give  the  same hash for the same Erlang term
              regardless of machine architecture and ERTS version (the BIF was introduced in ERTS
              5.2).  Range  can be between 1 and 2^32, the function returns a hash value for Term
              within the range 0..Range-1. When called without the Range argument, a value in the
              range 0..2^27-1 is returned.

              This  BIF  should  always  be used for hashing terms. It distributes small integers
              better than phash/2, and it is faster for bignums and binaries.

              Note that the range 0..Range-1 is different from the range of phash/2 (1..Range).

       pid_to_list(Pid) -> string()

              Types:

                 Pid = pid()

              Returns a string which corresponds to the text representation of Pid.

          Warning:
              This BIF is intended for debugging and for use in the Erlang operating  system.  It
              should not be used in application programs.

       port_close(Port) -> true

              Types:

                 Port = port() | atom()

              Closes  an  open  port.  Roughly  the same as Port ! {self(), close} except for the
              error behaviour (see below), being synchronous, and that the port  does  not  reply
              with  {Port,  closed}. Any process may close a port with port_close/1, not only the
              port owner (the connected process). If  the  calling  process  is  linked  to  port
              identified by Port, an exit signal due to that link will be received by the process
              prior to the return from port_close/1.

              For comparison: Port ! {self(), close} fails with badarg if Port cannot be sent  to
              (i.e.,  Port  refers  neither to a port nor to a process). If Port is a closed port
              nothing happens. If Port is an open port and the calling process is the port owner,
              the  port  replies  with  {Port, closed} when all buffers have been flushed and the
              port really closes, but if the calling process is not the port owner the port owner
              fails with badsig.

              Note  that  any process can close a port using Port ! {PortOwner, close} just as if
              it itself was the port owner, but the reply always goes to the port owner.

              As of OTP-R16 Port ! {PortOwner, close}  is  truly  asynchronous.  Note  that  this
              operation  has  always  been  documented  as  an  asynchronous operation, while the
              underlying implementation has been synchronous. port_close/1 is however still fully
              synchronous. This due to its error behavior.

              Failure:

                badarg:
                   If  Port  is  not  an identifier of an open port, or the registered name of an
                  open port. If the calling process  was  linked  to  the  previously  open  port
                  identified by Port, an exit signal due to this link was received by the process
                  prior to this exception.

       port_command(Port, Data) -> true

              Types:

                 Port = port() | atom()
                 Data = iodata()

              Sends data to a port. Same as Port ! {PortOwner, {command, Data}}  except  for  the
              error  behaviour  and being synchronous (see below). Any process may send data to a
              port with port_command/2, not only the port owner (the connected process).

              For comparison: Port ! {PortOwner, {command,  Data}}  fails  with  badarg  if  Port
              cannot  be  sent to (i.e., Port refers neither to a port nor to a process). If Port
              is a closed port the data message disappears without a sound. If Port is  open  and
              the  calling  process  is not the port owner, the port owner fails with badsig. The
              port owner fails with badsig also if Data is not a valid IO list.

              Note that any process can send to a port using Port ! {PortOwner, {command,  Data}}
              just as if it itself was the port owner.

              If  the  port  is busy, the calling process will be suspended until the port is not
              busy anymore.

              As of OTP-R16 Port ! {PortOwner, {command, Data}} is truly asynchronous. Note  that
              this  operation  has always been documented as an asynchronous operation, while the
              underlying implementation has been synchronous.  port_command/2  is  however  still
              fully synchronous. This due to its error behavior.

              Failures:

                badarg:
                   If  Port  is  not  an identifier of an open port, or the registered name of an
                  open port. If the calling process  was  linked  to  the  previously  open  port
                  identified by Port, an exit signal due to this link was received by the process
                  prior to this exception.

                badarg:
                   If Data is not a valid io list.

       port_command(Port, Data, OptionList) -> boolean()

              Types:

                 Port = port() | atom()
                 Data = iodata()
                 Option = force | nosuspend
                 OptionList = [Option]

              Sends data to a port. port_command(Port, Data, []) equals port_command(Port, Data).

              If the port command is aborted false is returned; otherwise, true is returned.

              If the port is busy, the calling process will be suspended until the  port  is  not
              busy anymore.

              Currently the following Options are valid:

                force:
                  The  calling  process  will  not be suspended if the port is busy; instead, the
                  port command is forced through. The call will fail with a notsup  exception  if
                  the  driver  of  the  port  does not support this. For more information see the
                  ERL_DRV_FLAG_SOFT_BUSY driver flag.

                nosuspend:
                  The calling process will not be suspended if the port  is  busy;  instead,  the
                  port command is aborted and false is returned.

          Note:
              More options may be added in the future.

              Failures:

                badarg:
                   If  Port  is  not  an identifier of an open port, or the registered name of an
                  open port. If the calling process  was  linked  to  the  previously  open  port
                  identified by Port, an exit signal due to this link was received by the process
                  prior to this exception.

                badarg:
                   If Data is not a valid io list.

                badarg:
                   If OptionList is not a valid option list.

                notsup:
                   If the force option has been passed, but the driver of the port does not allow
                  forcing through a busy port.

       port_connect(Port, Pid) -> true

              Types:

                 Port = port() | atom()
                 Pid = pid()

              Sets the port owner (the connected port) to Pid. Roughly the same as Port ! {Owner,
              {connect, Pid}} except for the following:

                * The error behavior differs, see below.

                * The port does not reply with {Port,connected}.

                * port_connect/1 is synchronous, see below.

                * The new port owner gets linked to the port.

              The old port owner stays linked to the port and have to call unlink(Port)  if  this
              is  not  desired.  Any  process  may  set  the  port  owner  to be any process with
              port_connect/2.

              For comparison: Port ! {self(), {connect, Pid}} fails with badarg if Port cannot be
              sent to (i.e., Port refers neither to a port nor to a process). If Port is a closed
              port nothing happens. If Port is an open port and the calling process is  the  port
              owner, the port replies with {Port, connected} to the old port owner. Note that the
              old port owner is still linked to the port, and that the new is not. If Port is  an
              open  port and the calling process is not the port owner, the port owner fails with
              badsig. The port owner fails with badsig also if Pid is not an existing local pid.

              Note that any process can set the port owner using  Port  !  {PortOwner,  {connect,
              Pid}}  just  as  if  it itself was the port owner, but the reply always goes to the
              port owner.

              As of OTP-R16 Port ! {PortOwner, {connect, Pid}} is truly asynchronous.  Note  that
              this  operation  has always been documented as an asynchronous operation, while the
              underlying implementation has been synchronous.  port_connect/2  is  however  still
              fully synchronous. This due to its error behavior.

              Failures:

                badarg:
                   If  Port  is  not  an identifier of an open port, or the registered name of an
                  open port. If the calling process  was  linked  to  the  previously  open  port
                  identified by Port, an exit signal due to this link was received by the process
                  prior to this exception.

                badarg:
                  If process identified by Pid is not an existing local process.

       port_control(Port, Operation, Data) -> iodata() | binary()

              Types:

                 Port = port() | atom()
                 Operation = integer()
                 Data = iodata()

              Performs a synchronous control operation on a port. The meaning  of  Operation  and
              Data  depends  on  the port, i.e., on the port driver. Not all port drivers support
              this control feature.

              Returns: a list of integers in the range 0 through 255, or a binary,  depending  on
              the port driver. The meaning of the returned data also depends on the port driver.

              Failure: badarg if Port is not an open port or the registered name of an open port,
              if Operation cannot fit in a 32-bit integer, if the port driver  does  not  support
              synchronous  control  operations,  or  if the port driver so decides for any reason
              (probably something wrong with Operation or Data).

       erlang:port_call(Port, Operation, Data) -> term()

              Types:

                 Port = port() | atom()
                 Operation = integer()
                 Data = term()

              Performs a synchronous call to a port. The meaning of Operation and Data depends on
              the port, i.e., on the port driver. Not all port drivers support this feature.

              Port is a port identifier, referring to a driver.

              Operation is an integer, which is passed on to the driver.

              Data  is  any Erlang term. This data is converted to binary term format and sent to
              the port.

              Returns: a term from the driver. The meaning of the returned data also  depends  on
              the port driver.

              Failures:

                badarg:
                   If  Port  is  not  an identifier of an open port, or the registered name of an
                  open port. If the calling process  was  linked  to  the  previously  open  port
                  identified by Port, an exit signal due to this link was received by the process
                  prior to this exception.

                badarg:
                   If Operation does not fit in a 32-bit integer.

                badarg:
                   If the port driver does not support synchronous control operations.

                badarg:
                   If the port driver so decides for any reason (probably  something  wrong  with
                  Operation, or Data).

       erlang:port_info(Port) -> Result

              Types:

                 Port = port() | atom()
                 ResultItem = {registered_name, RegisteredName :: atom()}
                            | {id, Index :: integer() >= 0}
                            | {connected, Pid :: pid()}
                            | {links, Pids :: [pid()]}
                            | {name, String :: string()}
                            | {input, Bytes :: integer() >= 0}
                            | {output, Bytes :: integer() >= 0}
                            | {os_pid, OsPid :: integer() >= 0 | undefined}
                 Result = [ResultItem] | undefined

              Returns  a  list containing tuples with information about the Port, or undefined if
              the port is not open. The order of the tuples is  not  defined,  nor  are  all  the
              tuples  mandatory. If undefined is returned and the calling process was linked to a
              previously open port identified by Port, an  exit  signal  due  to  this  link  was
              received by the process prior to the return from port_info/1.

              Currently   the  result  will  containt  information  about  the  following  Items:
              registered_name (if the port has a registered name), id,  connected,  links,  name,
              input, and output. For more information about the different Items, see port_info/2.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_info(Port, Item :: connected) ->
                           {connected, Pid} | undefined

              Types:

                 Port = port() | atom()
                 Pid = pid()

              Pid is the process identifier of the process connected to the port.

              If  the port identified by Port is not open, undefined is returned. If undefined is
              returned and the calling process was linked to a previously open port identified by
              Port,  an  exit  signal  due  to this link was received by the process prior to the
              return from port_info/2.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_info(Port, Item :: id) -> {id, Index} | undefined

              Types:

                 Port = port() | atom()
                 Index = integer() >= 0

              Index is the internal index of the port. This index may be used to separate ports.

              If the port identified by Port is not open, undefined is returned. If undefined  is
              returned and the calling process was linked to a previously open port identified by
              Port, an exit signal due to this link was received by  the  process  prior  to  the
              return from port_info/2.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_info(Port, Item :: input) ->
                           {input, Bytes} | undefined

              Types:

                 Port = port() | atom()
                 Bytes = integer() >= 0

              Bytes is the total number of bytes read from the port.

              If  the port identified by Port is not open, undefined is returned. If undefined is
              returned and the calling process was linked to a previously open port identified by
              Port,  an  exit  signal  due  to this link was received by the process prior to the
              return from port_info/2.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_info(Port, Item :: links) -> {links, Pids} | undefined

              Types:

                 Port = port() | atom()
                 Pids = [pid()]

              Pids is a list of the process identifiers of the processes that the port is  linked
              to.

              If  the port identified by Port is not open, undefined is returned. If undefined is
              returned and the calling process was linked to a previously open port identified by
              Port,  an  exit  signal  due  to this link was received by the process prior to the
              return from port_info/2.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_info(Port, Item :: locking) ->
                           {locking, Locking} | undefined

              Types:

                 Port = port() | atom()
                 Locking = false | port_level | driver_level

              Locking is currently either false (emulator without SMP support), port_level  (port
              specific  locking),  or  driver_level  (driver  specific  locking). Note that these
              results are highly implementation specific and might change in the future.

              If the port identified by Port is not open, undefined is returned. If undefined  is
              returned and the calling process was linked to a previously open port identified by
              Port, an exit signal due to this link was received by  the  process  prior  to  the
              return from port_info/2.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_info(Port, Item :: memory) ->
                           {memory, Bytes} | undefined

              Types:

                 Port = port() | atom()
                 Bytes = integer() >= 0

              Bytes  is  the  total  amount  of  memory, in bytes, allocated for this port by the
              runtime system. Note that the port itself might have allocated memory which is  not
              included in Bytes.

              If  the port identified by Port is not open, undefined is returned. If undefined is
              returned and the calling process was linked to a previously open port identified by
              Port,  an  exit  signal  due  to this link was received by the process prior to the
              return from port_info/2.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_info(Port, Item :: monitors) ->
                           {monitors, Monitors} | undefined

              Types:

                 Port = port() | atom()
                 Monitors = [{process, pid()}]

              Monitors represent processes that this port is monitoring.

              If the port identified by Port is not open, undefined is returned. If undefined  is
              returned and the calling process was linked to a previously open port identified by
              Port, an exit signal due to this link was received by  the  process  prior  to  the
              return from port_info/2.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_info(Port, Item :: name) -> {name, Name} | undefined

              Types:

                 Port = port() | atom()
                 Name = string()

              Name is the command name set by open_port/2.

              If  the port identified by Port is not open, undefined is returned. If undefined is
              returned and the calling process was linked to a previously open port identified by
              Port,  an  exit  signal  due  to this link was received by the process prior to the
              return from port_info/2.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_info(Port, Item :: os_pid) ->
                           {os_pid, OsPid} | undefined

              Types:

                 Port = port() | atom()
                 OsPid = integer() >= 0 | undefined

              OsPid is the process identifier (or equivalent)  of  an  OS  process  created  with
              open_port({spawn  |  spawn_executable,  Command},  Options). If the port is not the
              result of spawning an OS process, the value is undefined.

              If the port identified by Port is not open, undefined is returned. If undefined  is
              returned and the calling process was linked to a previously open port identified by
              Port, an exit signal due to this link was received by  the  process  prior  to  the
              return from port_info/2.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_info(Port, Item :: output) ->
                           {output, Bytes} | undefined

              Types:

                 Port = port() | atom()
                 Bytes = integer() >= 0

              Bytes  is the total number of bytes written to the port from Erlang processes using
              either port_command/2, port_command/3, or Port ! {Owner, {command, Data}.

              If the port identified by Port is not open, undefined is returned. If undefined  is
              returned and the calling process was linked to a previously open port identified by
              Port, an exit signal due to this link was received by  the  process  prior  to  the
              return from port_info/2.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_info(Port, Item :: parallelism) ->
                           {parallelism, Boolean} | undefined

              Types:

                 Port = port() | atom()
                 Boolean = boolean()

              Boolean  corresponds to the port parallelism hint being used by this port. For more
              information see the parallelism option of open_port/2.

       erlang:port_info(Port, Item :: queue_size) ->
                           {queue_size, Bytes} | undefined

              Types:

                 Port = port() | atom()
                 Bytes = integer() >= 0

              Bytes is the total amount of data, in bytes, queued by  the  port  using  the  ERTS
              driver queue implementation.

              If  the port identified by Port is not open, undefined is returned. If undefined is
              returned and the calling process was linked to a previously open port identified by
              Port,  an  exit  signal  due  to this link was received by the process prior to the
              return from port_info/2.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_info(Port, Item :: registered_name) ->
                           {registered_name, RegisteredName} |
                           [] |
                           undefined

              Types:

                 Port = port() | atom()
                 RegisteredName = atom()

              RegisteredName is the registered name of the port. If the port  has  no  registered
              name, [] is returned.

              If  the port identified by Port is not open, undefined is returned. If undefined is
              returned and the calling process was linked to a previously open port identified by
              Port,  an  exit  signal  due  to this link was received by the process prior to the
              return from port_info/2.

              Failure: badarg if Port is not a local port identifier, or an atom.

       erlang:port_to_list(Port) -> string()

              Types:

                 Port = port()

              Returns a  string  which  corresponds  to  the  text  representation  of  the  port
              identifier Port.

          Warning:
              This  BIF  is intended for debugging and for use in the Erlang operating system. It
              should not be used in application programs.

       erlang:ports() -> [port()]

              Returns a list of  port  identifiers  corresponding  to  all  the  ports  currently
              existing on the local node.

              Note that a port that is exiting, exists but is not open.

       pre_loaded() -> [module()]

              Returns a list of Erlang modules which are pre-loaded in the system. As all loading
              of code is done through the file system, the file  system  must  have  been  loaded
              previously. Hence, at least the module init must be pre-loaded.

       erlang:process_display(Pid, Type) -> true

              Types:

                 Pid = pid()
                 Type = backtrace

              Writes  information  about  the  local process Pid on standard error. The currently
              allowed value for the atom Type is backtrace, which shows the contents of the  call
              stack,  including  information  about  the  call  chain,  with the current function
              printed first. The format of the output is not further defined.

       process_flag(Flag :: trap_exit, Boolean) -> OldBoolean

              Types:

                 Boolean = OldBoolean = boolean()

              When trap_exit is set to true, exit signals arriving to a process are converted  to
              {'EXIT',  From,  Reason}  messages,  which can be received as ordinary messages. If
              trap_exit is set to false, the process exits if it receives an  exit  signal  other
              than  normal and the exit signal is propagated to its linked processes. Application
              processes should normally not trap exits.

              Returns the old value of the flag.

              See also exit/2.

       process_flag(Flag :: error_handler, Module) -> OldModule

              Types:

                 Module = OldModule = atom()

              This is used by a process to redefine the  error  handler  for  undefined  function
              calls  and  undefined registered processes. Inexperienced users should not use this
              flag since code auto-loading is dependent on the correct  operation  of  the  error
              handling module.

              Returns the old value of the flag.

       process_flag(Flag :: min_heap_size, MinHeapSize) -> OldMinHeapSize

              Types:

                 MinHeapSize = OldMinHeapSize = integer() >= 0

              This changes the minimum heap size for the calling process.

              Returns the old value of the flag.

       process_flag(Flag :: min_bin_vheap_size, MinBinVHeapSize) ->
                       OldMinBinVHeapSize

              Types:

                 MinBinVHeapSize = OldMinBinVHeapSize = integer() >= 0

              This changes the minimum binary virtual heap size for the calling process.

              Returns the old value of the flag.

       process_flag(Flag :: priority, Level) -> OldLevel

              Types:

                 Level = OldLevel = priority_level()
                 priority_level() = low | normal | high | max

              This sets the process priority. Level is an atom. There are currently four priority
              levels: low, normal, high, and max. The default priority level is normal. NOTE: The
              max  priority  level is reserved for internal use in the Erlang runtime system, and
              should not be used by others.

              Internally in each priority level processes are scheduled in a round robin fashion.

              Execution of processes on priority normal and priority  low  will  be  interleaved.
              Processes  on  priority  low  will  be  selected for execution less frequently than
              processes on priority normal.

              When there are runnable processes on priority high no processes on priority low, or
              normal  will be selected for execution. Note, however, that this does not mean that
              no processes on priority low, or  normal  will  be  able  to  run  when  there  are
              processes  on  priority  high running. On the runtime system with SMP support there
              might be more processes running in parallel than processes on priority high,  i.e.,
              a low, and a high priority process might execute at the same time.

              When  there  are  runnable  processes on priority max no processes on priority low,
              normal, or high will  be  selected  for  execution.  As  with  the  high  priority,
              processes  on lower priorities might execute in parallel with processes on priority
              max.

              Scheduling is preemptive. Regardless of priority, a process is  preempted  when  it
              has  consumed  more  than a certain amount of reductions since the last time it was
              selected for execution.

              NOTE: You should not depend on the scheduling to remain exactly  as  it  is  today.
              Scheduling,  at  least on the runtime system with SMP support, is very likely to be
              modified in the future in order to better utilize available processor cores.

              There is currently no automatic mechanism for avoiding priority inversion, such  as
              priority  inheritance, or priority ceilings. When using priorities you have to take
              this into account and handle such scenarios by yourself.

              Making calls from a high priority process into code that  you  don't  have  control
              over  may  cause  the  high  priority  process  to  wait for a processes with lower
              priority, i.e., effectively decreasing the priority of the  high  priority  process
              during  the call. Even if this isn't the case with one version of the code that you
              don't have under your control, it might be the case in a future version of it. This
              might,  for example, happen if a high priority process triggers code loading, since
              the code server runs on priority normal.

              Other priorities than normal are normally not needed.  When  other  priorities  are
              used,  they  need  to  be used with care, especially the high priority must be used
              with care. A process on high priority should only perform work for short periods of
              time.  Busy  looping  for long periods of time in a high priority process will most
              likely cause problems, since there are important servers in OTP running on priority
              normal.

              Returns the old value of the flag.

       process_flag(Flag :: save_calls, N) -> OldN

              Types:

                 N = OldN = 0..10000

              N must be an integer in the interval 0..10000. If N > 0, call saving is made active
              for the process, which means that  information  about  the  N  most  recent  global
              function  calls,  BIF  calls, sends and receives made by the process are saved in a
              list, which can be retrieved with process_info(Pid, last_calls). A global  function
              call  is  one  in  which the module of the function is explicitly mentioned. Only a
              fixed amount of information  is  saved:  a  tuple  {Module,  Function,  Arity}  for
              function  calls,  and  the  mere  atoms  send,  'receive' and timeout for sends and
              receives ('receive' when a message is received and timeout  when  a  receive  times
              out).  If  N  =  0,  call saving is disabled for the process, which is the default.
              Whenever the size of the call saving list is set, its contents are reset.

              Returns the old value of the flag.

       process_flag(Flag :: sensitive, Boolean) -> OldBoolean

              Types:

                 Boolean = OldBoolean = boolean()

              Set or clear the sensitive flag for the current process. When a  process  has  been
              marked  as sensitive by calling process_flag(sensitive, true), features in the run-
              time system that can be used for examining the data and/or  inner  working  of  the
              process are silently disabled.

              Features that are disabled include (but are not limited to) the following:

              Tracing: Trace flags can still be set for the process, but no trace messages of any
              kind will be generated. (If the sensitive flag is turned off, trace  messages  will
              again be generated if there are any trace flags set.)

              Sequential  tracing: The sequential trace token will be propagated as usual, but no
              sequential trace messages will be generated.

              process_info/1,2 cannot be used to read  out  the  message  queue  or  the  process
              dictionary (both will be returned as empty lists).

              Stack back-traces cannot be displayed for the process.

              In crash dumps, the stack, messages, and the process dictionary will be omitted.

              If  {save_calls,N} has been set for the process, no function calls will be saved to
              the call saving list. (The call saving list will not be cleared; furthermore, send,
              receive, and timeout events will still be added to the list.)

              Returns the old value of the flag.

       process_flag(Pid, Flag, Value) -> OldValue

              Types:

                 Pid = pid()
                 Flag = save_calls
                 Value = OldValue = integer() >= 0

              Sets  certain  flags  for  the  process  Pid, in the same manner as process_flag/2.
              Returns the old value of the flag. The allowed values for Flag are only a subset of
              those allowed in process_flag/2, namely: save_calls.

              Failure: badarg if Pid is not a local process.

       process_info(Pid) -> Info

              Types:

                 Pid = pid()
                 Info = [InfoTuple] | undefined
                 InfoTuple = process_info_result_item()
                 process_info_result_item() = {backtrace, Bin :: binary()}
                                            | {binary,
                                               BinInfo ::
                                                   [{integer() >= 0,
                                                     integer() >= 0,
                                                     integer() >= 0}]}
                                            | {catchlevel,
                                               CatchLevel :: integer() >= 0}
                                            | {current_function,
                                               {Module :: module(),
                                                Function :: atom(),
                                                Arity :: arity()}}
                                            | {current_location,
                                               {Module :: module(),
                                                Function :: atom(),
                                                Arity :: arity(),
                                                Location ::
                                                    [{file,
                                                      Filename :: string()} |
                                                     {line,
                                                      Line :: integer() >= 1}]}}
                                            | {current_stacktrace,
                                               Stack :: [stack_item()]}
                                            | {dictionary,
                                               Dictionary ::
                                                   [{Key :: term(),
                                                     Value :: term()}]}
                                            | {error_handler,
                                               Module :: module()}
                                            | {garbage_collection,
                                               GCInfo ::
                                                   [{atom(), integer() >= 0}]}
                                            | {group_leader,
                                               GroupLeader :: pid()}
                                            | {heap_size,
                                               Size :: integer() >= 0}
                                            | {initial_call, mfa()}
                                            | {links,
                                               PidsAndPorts :: [pid() | port()]}
                                            | {last_calls,
                                               false | (Calls :: [mfa()])}
                                            | {memory,
                                               Size :: integer() >= 0}
                                            | {message_queue_len,
                                               MessageQueueLen ::
                                                   integer() >= 0}
                                            | {messages,
                                               MessageQueue :: [term()]}
                                            | {min_heap_size,
                                               MinHeapSize :: integer() >= 0}
                                            | {min_bin_vheap_size,
                                               MinBinVHeapSize ::
                                                   integer() >= 0}
                                            | {monitored_by, Pids :: [pid()]}
                                            | {monitors,
                                               Monitors ::
                                                   [{process,
                                                     Pid :: pid()
                                                          | {RegName :: atom(),
                                                             Node :: node()}}]}
                                            | {priority,
                                               Level :: priority_level()}
                                            | {reductions,
                                               Number :: integer() >= 0}
                                            | {registered_name, Atom :: atom()}
                                            | {sequential_trace_token,
                                               [] |
                                               (SequentialTraceToken :: term())}
                                            | {stack_size,
                                               Size :: integer() >= 0}
                                            | {status,
                                               Status :: exiting
                                                       | garbage_collecting
                                                       | waiting
                                                       | running
                                                       | runnable
                                                       | suspended}
                                            | {suspending,
                                               SuspendeeList ::
                                                   [{Suspendee :: pid(),
                                                     ActiveSuspendCount ::
                                                         integer() >= 0,
                                                     OutstandingSuspendCount ::
                                                         integer() >= 0}]}
                                            | {total_heap_size,
                                               Size :: integer() >= 0}
                                            | {trace,
                                               InternalTraceFlags ::
                                                   integer() >= 0}
                                            | {trap_exit, Boolean :: boolean()}
                 priority_level() = low | normal | high | max
                 stack_item() =
                     {Module :: module(),
                      Function :: atom(),
                      Arity :: arity() | (Args :: [term()]),
                      Location ::
                          [{file, Filename :: string()} |
                           {line, Line :: integer() >= 1}]}

              Returns  a  list  containing  InfoTuples  with  miscellaneous information about the
              process identified by Pid, or undefined if the process is not alive.

              The order of the InfoTuples is not defined, nor are all the  InfoTuples  mandatory.
              The  InfoTuples  part  of the result may be changed without prior notice. Currently
              InfoTuples with the following items  are  part  of  the  result:  current_function,
              initial_call,  status,  message_queue_len,  messages, links, dictionary, trap_exit,
              error_handler,  priority,  group_leader,  total_heap_size,  heap_size,  stack_size,
              reductions,  and  garbage_collection.  If  the  process  identified  by  Pid  has a
              registered name also an InfoTuple with the item registered_name will appear.

              See process_info/2 for information about specific InfoTuples.

          Warning:
              This BIF is intended for debugging only, use process_info/2 for all other purposes.

              Failure: badarg if Pid is not a local process.

       process_info(Pid, Item) -> InfoTuple | [] | undefined

       process_info(Pid, ItemList) -> InfoTupleList | [] | undefined

              Types:

                 Pid = pid()
                 ItemList = [Item]
                 Item = process_info_item()
                 InfoTupleList = [InfoTuple]
                 InfoTuple = process_info_result_item()
                 process_info_item() = backtrace
                                     | binary
                                     | catchlevel
                                     | current_function
                                     | current_location
                                     | current_stacktrace
                                     | dictionary
                                     | error_handler
                                     | garbage_collection
                                     | group_leader
                                     | heap_size
                                     | initial_call
                                     | links
                                     | last_calls
                                     | memory
                                     | message_queue_len
                                     | messages
                                     | min_heap_size
                                     | min_bin_vheap_size
                                     | monitored_by
                                     | monitors
                                     | priority
                                     | reductions
                                     | registered_name
                                     | sequential_trace_token
                                     | stack_size
                                     | status
                                     | suspending
                                     | total_heap_size
                                     | trace
                                     | trap_exit
                 process_info_result_item() = {backtrace, Bin :: binary()}
                                            | {binary,
                                               BinInfo ::
                                                   [{integer() >= 0,
                                                     integer() >= 0,
                                                     integer() >= 0}]}
                                            | {catchlevel,
                                               CatchLevel :: integer() >= 0}
                                            | {current_function,
                                               {Module :: module(),
                                                Function :: atom(),
                                                Arity :: arity()}}
                                            | {current_location,
                                               {Module :: module(),
                                                Function :: atom(),
                                                Arity :: arity(),
                                                Location ::
                                                    [{file,
                                                      Filename :: string()} |
                                                     {line,
                                                      Line :: integer() >= 1}]}}
                                            | {current_stacktrace,
                                               Stack :: [stack_item()]}
                                            | {dictionary,
                                               Dictionary ::
                                                   [{Key :: term(),
                                                     Value :: term()}]}
                                            | {error_handler,
                                               Module :: module()}
                                            | {garbage_collection,
                                               GCInfo ::
                                                   [{atom(), integer() >= 0}]}
                                            | {group_leader,
                                               GroupLeader :: pid()}
                                            | {heap_size,
                                               Size :: integer() >= 0}
                                            | {initial_call, mfa()}
                                            | {links,
                                               PidsAndPorts :: [pid() | port()]}
                                            | {last_calls,
                                               false | (Calls :: [mfa()])}
                                            | {memory,
                                               Size :: integer() >= 0}
                                            | {message_queue_len,
                                               MessageQueueLen ::
                                                   integer() >= 0}
                                            | {messages,
                                               MessageQueue :: [term()]}
                                            | {min_heap_size,
                                               MinHeapSize :: integer() >= 0}
                                            | {min_bin_vheap_size,
                                               MinBinVHeapSize ::
                                                   integer() >= 0}
                                            | {monitored_by, Pids :: [pid()]}
                                            | {monitors,
                                               Monitors ::
                                                   [{process,
                                                     Pid :: pid()
                                                          | {RegName :: atom(),
                                                             Node :: node()}}]}
                                            | {priority,
                                               Level :: priority_level()}
                                            | {reductions,
                                               Number :: integer() >= 0}
                                            | {registered_name, Atom :: atom()}
                                            | {sequential_trace_token,
                                               [] |
                                               (SequentialTraceToken :: term())}
                                            | {stack_size,
                                               Size :: integer() >= 0}
                                            | {status,
                                               Status :: exiting
                                                       | garbage_collecting
                                                       | waiting
                                                       | running
                                                       | runnable
                                                       | suspended}
                                            | {suspending,
                                               SuspendeeList ::
                                                   [{Suspendee :: pid(),
                                                     ActiveSuspendCount ::
                                                         integer() >= 0,
                                                     OutstandingSuspendCount ::
                                                         integer() >= 0}]}
                                            | {total_heap_size,
                                               Size :: integer() >= 0}
                                            | {trace,
                                               InternalTraceFlags ::
                                                   integer() >= 0}
                                            | {trap_exit, Boolean :: boolean()}
                 stack_item() =
                     {Module :: module(),
                      Function :: atom(),
                      Arity :: arity() | (Args :: [term()]),
                      Location ::
                          [{file, Filename :: string()} |
                           {line, Line :: integer() >= 1}]}
                 priority_level() = low | normal | high | max

              Returns information about the process identified by Pid as specified by the Item or
              the ItemList, or undefined if the process is not alive.

              If  the  process  is  alive  and  a single Item is given, the returned value is the
              corresponding InfoTuple unless Item =:= registered_name  and  the  process  has  no
              registered  name.  In  this  case  []  is returned. This strange behavior is due to
              historical reasons, and is kept for backward compatibility.

              If an ItemList is given, the result is an  InfoTupleList.  The  InfoTuples  in  the
              InfoTupleList  will  appear  with  the corresponding Items in the same order as the
              Items appeared in the ItemList. Valid  Items  may  appear  multiple  times  in  the
              ItemList.

          Note:
              If  registered_name is part of an ItemList and the process has no name registered a
              {registered_name, []} InfoTuple will appear in the  resulting  InfoTupleList.  This
              behavior  is  different  than  when a single Item =:= registered_name is given, and
              than when process_info/1 is used.

              Currently the following InfoTuples with corresponding Items are valid:

                {backtrace, Bin}:
                  The  binary  Bin  contains  the   same   information   as   the   output   from
                  erlang:process_display(Pid,  backtrace).  Use  binary_to_list/1  to  obtain the
                  string of characters from the binary.

                {binary, BinInfo}:
                  BinInfo is a list containing miscellaneous information about binaries currently
                  being  referred  to  by  this process. This InfoTuple may be changed or removed
                  without prior notice.

                {catchlevel, CatchLevel}:
                  CatchLevel is the number of currently active  catches  in  this  process.  This
                  InfoTuple may be changed or removed without prior notice.

                {current_function, {Module, Function, Arity}}:
                  Module, Function, Arity is the current function call of the process.

                {current_location, {Module, Function, Arity, Location}}:
                  Module,  Function,  Arity is the current function call of the process. Location
                  is a list of two-tuples that describes the location in the source code.

                {current_stacktrace, Stack}:
                  Return the current call stack back-trace (stacktrace) of the process. The stack
                  has the same format as returned by erlang:get_stacktrace/0.

                {dictionary, Dictionary}:
                  Dictionary is the dictionary of the process.

                {error_handler, Module}:
                  Module  is the error handler module used by the process (for undefined function
                  calls, for example).

                {garbage_collection, GCInfo}:
                  GCInfo is  a  list  which  contains  miscellaneous  information  about  garbage
                  collection for this process. The content of GCInfo may be changed without prior
                  notice.

                {group_leader, GroupLeader}:
                  GroupLeader is group leader for the IO of the process.

                {heap_size, Size}:
                  Size is the size in words of youngest heap  generation  of  the  process.  This
                  generation  currently  include  the  stack  of the process. This information is
                  highly implementation dependent, and may change if the implementation change.

                {initial_call, {Module, Function, Arity}}:
                  Module, Function, Arity is the initial function call with which the process was
                  spawned.

                {links, PidsAndPorts}:
                  PidsAndPorts is a list of pids and port identifiers, with processes or ports to
                  which the process has a link.

                {last_calls, false|Calls}:
                  The value is  false  if  call  saving  is  not  active  for  the  process  (see
                  process_flag/3).  If  call  saving  is active, a list is returned, in which the
                  last element is the most recent called.

                {memory, Size}:
                  Size is the size in bytes of the process. This includes call  stack,  heap  and
                  internal structures.

                {message_queue_len, MessageQueueLen}:
                  MessageQueueLen is the number of messages currently in the message queue of the
                  process. This is the length of the list MessageQueue returned as the info  item
                  messages (see below).

                {messages, MessageQueue}:
                  MessageQueue  is a list of the messages to the process, which have not yet been
                  processed.

                {min_heap_size, MinHeapSize}:
                  MinHeapSize is the minimum heap size for the process.

                {min_bin_vheap_size, MinBinVHeapSize}:
                  MinBinVHeapSize is the minimum binary virtual heap size for the process.

                {monitored_by, Pids}:
                  A list of pids that are monitoring the process (with monitor/2).

                {monitors, Monitors}:
                  A list of monitors (started by monitor/2) that are active for the process.  For
                  a  local  process  monitor or a remote process monitor by pid, the list item is
                  {process, Pid}, and for a remote process monitor by  name,  the  list  item  is
                  {process, {RegName, Node}}.

                {priority, Level}:
                  Level  is  the  current priority level for the process. For more information on
                  priorities see process_flag(priority, Level).

                {reductions, Number}:
                  Number is the number of reductions executed by the process.

                {registered_name, Atom}:
                  Atom is the registered name of the process. If the process  has  no  registered
                  name, this tuple is not present in the list.

                {sequential_trace_token, [] | SequentialTraceToken}:
                  SequentialTraceToken the sequential trace token for the process. This InfoTuple
                  may be changed or removed without prior notice.

                {stack_size, Size}:
                  Size is the stack size of the process in words.

                {status, Status}:
                  Status is the status of the process.  Status  is  exiting,  garbage_collecting,
                  waiting  (for  a message), running, runnable (ready to run, but another process
                  is  running),  or  suspended  (suspended  on  a   "busy"   port   or   by   the
                  erlang:suspend_process/[1,2] BIF).

                {suspending, SuspendeeList}:
                  SuspendeeList     is     a     list    of    {Suspendee,    ActiveSuspendCount,
                  OutstandingSuspendCount} tuples. Suspendee is the pid of a  process  that  have
                  been  or  is  to  be  suspended  by  the  process  identified  by  Pid  via the
                  erlang:suspend_process/2   BIF,   or    the    erlang:suspend_process/1    BIF.
                  ActiveSuspendCount  is  the number of times the Suspendee has been suspended by
                  Pid. OutstandingSuspendCount  is  the  number  of  not  yet  completed  suspend
                  requests  sent  by  Pid.  That  is,  if  ActiveSuspendCount =/= 0, Suspendee is
                  currently in the suspended state, and  if  OutstandingSuspendCount  =/=  0  the
                  asynchronous option of erlang:suspend_process/2 has been used and the suspendee
                  has not yet been  suspended  by  Pid.  Note  that  the  ActiveSuspendCount  and
                  OutstandingSuspendCount  are not the total suspend count on Suspendee, only the
                  parts contributed by Pid.

                {total_heap_size, Size}:
                  Size is the total size in words of all heap  fragments  of  the  process.  This
                  currently include the stack of the process.

                {trace, InternalTraceFlags}:
                  InternalTraceFlags  is  an  integer  representing  internal trace flag for this
                  process. This InfoTuple may be changed or removed without prior notice.

                {trap_exit, Boolean}:
                  Boolean is true if the process is trapping exits, otherwise it is false.

              Note however, that not all implementations support every one of the above Items.

              Failure: badarg if Pid is not a local process, or if Item is not a valid Item.

       processes() -> [pid()]

              Returns a list of process identifiers corresponding to all the processes  currently
              existing on the local node.

              Note   that   a   process   that  is  exiting,  exists  but  is  not  alive,  i.e.,
              is_process_alive/1 will return false for a process that is exiting, but its process
              identifier will be part of the result returned from processes/0.

              > processes().
              [<0.0.0>,<0.2.0>,<0.4.0>,<0.5.0>,<0.7.0>,<0.8.0>]

       purge_module(Module) -> true

              Types:

                 Module = atom()

              Removes  old  code for Module. Before this BIF is used, erlang:check_process_code/2
              should be called to check that no processes are executing old code in the module.

          Warning:
              This BIF is intended for the code server (see code(3erl)) and should  not  be  used
              elsewhere.

              Failure: badarg if there is no old code for Module.

       put(Key, Val) -> term()

              Types:

                 Key = Val = term()

              Adds  a  new  Key  to  the  process  dictionary, associated with the value Val, and
              returns undefined. If Key already exists, the old value is deleted and replaced  by
              Val and the function returns the old value.

          Note:
              The  values  stored  when  put is evaluated within the scope of a catch will not be
              retracted if a throw is evaluated, or if an error occurs.

              > X = put(name, walrus), Y = put(name, carpenter),
              Z = get(name),
              {X, Y, Z}.
              {undefined,walrus,carpenter}

       erlang:raise(Class, Reason, Stacktrace) -> no_return()

              Types:

                 Class = error | exit | throw
                 Reason = term()
                 Stacktrace = raise_stacktrace()
                 raise_stacktrace() = [{module(), atom(), arity() | [term()]} |
                                       {function(), [term()]}]
                                    | [{module(),
                                        atom(),
                                        arity() | [term()],
                                        [{atom(), term()}]} |
                                       {function(),
                                        [term()],
                                        [{atom(), term()}]}]

              Stops the execution of the calling process with an exception of given class, reason
              and call stack backtrace (stacktrace).

          Warning:
              This  BIF  is intended for debugging and for use in the Erlang operating system. In
              general, it should be avoided in applications, unless you know very well  what  you
              are doing.

              Class  is  one  of  error,  exit  or  throw,  so  if it were not for the stacktrace
              erlang:raise(Class, Reason,  Stacktrace)  is  equivalent  to  erlang:Class(Reason).
              Reason is any term and Stacktrace is a list as returned from get_stacktrace(), that
              is a list of 4-tuples {Module, Function, Arity | Args, Location} where  Module  and
              Function  are  atoms and the third element is an integer arity or an argument list.
              The stacktrace may also contain {Fun, Args, Location} tuples where Fun is  a  local
              fun and Args is an argument list.

              The  Location  element  at  the  end  is  optional.  Omitting  it  is equivalent to
              specifying an empty list.

              The stacktrace is used as the exception stacktrace for the calling process; it will
              be truncated to the current maximum stacktrace depth.

              Because  evaluating this function causes the process to terminate, it has no return
              value - unless the arguments are invalid, in which case the  function  returns  the
              error  reason,  that is badarg. If you want to be really sure not to return you can
              call  error(erlang:raise(Class,  Reason,  Stacktrace))  and  hope  to   distinguish
              exceptions later.

       erlang:read_timer(TimerRef) -> integer() >= 0 | false

              Types:

                 TimerRef = reference()

              TimerRef    is    a    timer   reference   returned   by   erlang:send_after/3   or
              erlang:start_timer/3. If the timer is active, the  function  returns  the  time  in
              milliseconds  left  until  the timer will expire, otherwise false (which means that
              TimerRef was never a timer, that it has been cancelled,  or  that  it  has  already
              delivered its message).

              See also erlang:send_after/3, erlang:start_timer/3, and erlang:cancel_timer/1.

       erlang:ref_to_list(Ref) -> string()

              Types:

                 Ref = reference()

              Returns a string which corresponds to the text representation of Ref.

          Warning:
              This  BIF  is intended for debugging and for use in the Erlang operating system. It
              should not be used in application programs.

       register(RegName, PidOrPort) -> true

              Types:

                 RegName = atom()
                 PidOrPort = port() | pid()

              Associates the name RegName with a pid or a port identifier. RegName, which must be
              an  atom,  can  be  used  instead of the pid / port identifier in the send operator
              (RegName ! Message).

              > register(db, Pid).
              true

              Failure: badarg if PidOrPort is not an existing, local process or port, if  RegName
              is  already  in  use,  if  the process or port is already registered (already has a
              name), or if RegName is the atom undefined.

       registered() -> [RegName]

              Types:

                 RegName = atom()

              Returns a list of names which have been registered using register/2.

              > registered().
              [code_server, file_server, init, user, my_db]

       erlang:resume_process(Suspendee) -> true

              Types:

                 Suspendee = pid()

              Decreases the suspend count on  the  process  identified  by  Suspendee.  Suspendee
              should   previously   have   been   suspended   via   erlang:suspend_process/2,  or
              erlang:suspend_process/1 by the process  calling  erlang:resume_process(Suspendee).
              When  the  suspend  count on Suspendee reach zero, Suspendee will be resumed, i.e.,
              the state of the Suspendee is changed from suspended into the state  Suspendee  was
              in before it was suspended.

          Warning:
              This BIF is intended for debugging only.

              Failures:

                badarg:
                   If Suspendee isn't a process identifier.

                badarg:
                   If  the  process  calling erlang:resume_process/1 had not previously increased
                  the suspend count on the process identified by Suspendee.

                badarg:
                   If the process identified by Suspendee is not alive.

       round(Number) -> integer()

              Types:

                 Number = number()

              Returns an integer by rounding Number.

              > round(5.5).
              6

              Allowed in guard tests.

       self() -> pid()

              Returns the pid (process identifier) of the calling process.

              > self().
              <0.26.0>

              Allowed in guard tests.

       erlang:send(Dest, Msg) -> Msg

              Types:

                 Dest = dst()
                 Msg = term()
                 dst() = pid()
                       | port()
                       | (RegName :: atom())
                       | {RegName :: atom(), Node :: node()}

              Sends a message and returns Msg. This is the same as Dest ! Msg.

              Dest may be a remote or local pid, a (local) port, a locally registered name, or  a
              tuple {RegName, Node} for a registered name at another node.

       erlang:send(Dest, Msg, Options) -> Res

              Types:

                 Dest = dst()
                 Msg = term()
                 Options = [nosuspend | noconnect]
                 Res = ok | nosuspend | noconnect
                 dst() = pid()
                       | port()
                       | (RegName :: atom())
                       | {RegName :: atom(), Node :: node()}

              Sends  a message and returns ok, or does not send the message but returns something
              else   (see   below).   Otherwise   the   same   as   erlang:send/2.    See    also
              erlang:send_nosuspend/2,3. for more detailed explanation and warnings.

              The possible options are:

                nosuspend:
                  If  the sender would have to be suspended to do the send, nosuspend is returned
                  instead.

                noconnect:
                  If the destination node would have to be auto-connected before doing the  send,
                  noconnect is returned instead.

          Warning:
              As with erlang:send_nosuspend/2,3: Use with extreme care!

       erlang:send_after(Time, Dest, Msg) -> TimerRef

              Types:

                 Time = integer() >= 0
                   0 <= Time <= 4294967295
                 Dest = pid() | atom()
                 Msg = term()
                 TimerRef = reference()

              Starts a timer which will send the message Msg to Dest after Time milliseconds.

              If Dest is a pid() it has to be a pid() of a local process, dead or alive.

              The Time value can, in the current implementation, not be greater than 4294967295.

              If  Dest  is  an atom(), it is supposed to be the name of a registered process. The
              process referred to by the name is looked up at the time of delivery. No  error  is
              given if the name does not refer to a process.

              If  Dest  is  a  pid(),  the  timer  will  be automatically canceled if the process
              referred to by the pid() is not alive, or when the process exits. This feature  was
              introduced  in  erts  version  5.4.11.  Note  that timers will not be automatically
              canceled when Dest is an atom.

              See also erlang:start_timer/3, erlang:cancel_timer/1, and erlang:read_timer/1.

              Failure: badarg if the arguments does not satisfy the requirements specified above.

       erlang:send_nosuspend(Dest, Msg) -> boolean()

              Types:

                 Dest = dst()
                 Msg = term()
                 dst() = pid()
                       | port()
                       | (RegName :: atom())
                       | {RegName :: atom(), Node :: node()}

              The same as erlang:send(Dest, Msg, [nosuspend]), but returns true  if  the  message
              was sent and false if the message was not sent because the sender would have had to
              be suspended.

              This function is intended for send operations towards  an  unreliable  remote  node
              without ever blocking the sending (Erlang) process. If the connection to the remote
              node (usually not a real Erlang  node,  but  a  node  written  in  C  or  Java)  is
              overloaded, this function will not send the message but return false instead.

              The  same  happens,  if  Dest  refers  to  a local port that is busy. For all other
              destinations (allowed for the ordinary send operator '!') this function  sends  the
              message and returns true.

              This  function  is  only  to  be  used  in  very rare circumstances where a process
              communicates with Erlang nodes that can disappear without any trace causing the TCP
              buffers and the drivers queue to be over-full before the node will actually be shut
              down (due to tick timeouts) by net_kernel. The normal reaction to  take  when  this
              happens is some kind of premature shutdown of the other node.

              Note  that  ignoring the return value from this function would result in unreliable
              message passing, which is  contradictory  to  the  Erlang  programming  model.  The
              message is not sent if this function returns false.

              Note  also  that in many systems, transient states of overloaded queues are normal.
              The fact that this function returns false does not in any way mean that  the  other
              node  is  guaranteed to be non-responsive, it could be a temporary overload. Also a
              return value of true does only mean that the message could be  sent  on  the  (TCP)
              channel  without  blocking,  the  message  is not guaranteed to have arrived at the
              remote node. Also in the case of a disconnected  non-responsive  node,  the  return
              value  is  true (mimics the behaviour of the ! operator). The expected behaviour as
              well as the actions to take when the function returns  false  are  application  and
              hardware specific.

          Warning:
              Use with extreme care!

       erlang:send_nosuspend(Dest, Msg, Options) -> boolean()

              Types:

                 Dest = dst()
                 Msg = term()
                 Options = [noconnect]
                 dst() = pid()
                       | port()
                       | (RegName :: atom())
                       | {RegName :: atom(), Node :: node()}

              The  same as erlang:send(Dest, Msg, [nosuspend | Options]), but with boolean return
              value.

              This function behaves like erlang:send_nosuspend/2), but takes a third parameter, a
              list  of  options.  The  only currently implemented option is noconnect. The option
              noconnect makes the function return false if  the  remote  node  is  not  currently
              reachable by the local node. The normal behaviour is to try to connect to the node,
              which may stall the process for a shorter period. The use of the  noconnect  option
              makes  it  possible  to be absolutely sure not to get even the slightest delay when
              sending to a remote process. This is  especially  useful  when  communicating  with
              nodes  who  expect  to  always  be  the connecting part (i.e. nodes written in C or
              Java).

              Whenever the function returns false (either when a  suspend  would  occur  or  when
              noconnect  was  specified  and  the node was not already connected), the message is
              guaranteed not to have been sent.

          Warning:
              Use with extreme care!

       erlang:set_cookie(Node, Cookie) -> true

              Types:

                 Node = node()
                 Cookie = atom()

              Sets the magic cookie of Node to the atom Cookie. If Node is the  local  node,  the
              function also sets the cookie of all other unknown nodes to Cookie (see Distributed
              Erlang in the Erlang Reference Manual).

              Failure: function_clause if the local node is not alive.

       setelement(Index, Tuple1, Value) -> Tuple2

              Types:

                 Index = integer() >= 1
                   1..tuple_size(Tuple1)
                 Tuple1 = Tuple2 = tuple()
                 Value = term()

              Returns a tuple which is a copy of the argument Tuple1 with the  element  given  by
              the integer argument Index (the first element is the element with index 1) replaced
              by the argument Value.

              > setelement(2, {10, green, bottles}, red).
              {10,red,bottles}

       size(Item) -> integer() >= 0

              Types:

                 Item = tuple() | binary()

              Returns an integer which is the size of the argument Item, which must be  either  a
              tuple or a binary.

              > size({morni, mulle, bwange}).
              3

              Allowed in guard tests.

       spawn(Fun) -> pid()

              Types:

                 Fun = function()

              Returns  the  pid  of  a new process started by the application of Fun to the empty
              list []. Otherwise works like spawn/3.

       spawn(Node, Fun) -> pid()

              Types:

                 Node = node()
                 Fun = function()

              Returns the pid of a new process started by the application of  Fun  to  the  empty
              list [] on Node. If Node does not exist, a useless pid is returned. Otherwise works
              like spawn/3.

       spawn(Module, Function, Args) -> pid()

              Types:

                 Module = module()
                 Function = atom()
                 Args = [term()]

              Returns the pid of a new process started by the application of  Module:Function  to
              Args.  The  new process created will be placed in the system scheduler queue and be
              run some time later.

              error_handler:undefined_function(Module, Function, Args) is evaluated  by  the  new
              process  if  Module:Function/Arity  does  not  exist  (where Arity is the length of
              Args). The error handler can be redefined (see process_flag/2). If error_handler is
              undefined,  or  the user has redefined the default error_handler its replacement is
              undefined, a failure with the reason undef will occur.

              > spawn(speed, regulator, [high_speed, thin_cut]).
              <0.13.1>

       spawn(Node, Module, Function, Args) -> pid()

              Types:

                 Node = node()
                 Module = module()
                 Function = atom()
                 Args = [term()]

              Returns the pid of a new process started by the application of  Module:Function  to
              Args  on  Node. If Node does not exists, a useless pid is returned. Otherwise works
              like spawn/3.

       spawn_link(Fun) -> pid()

              Types:

                 Fun = function()

              Returns the pid of a new process started by the application of  Fun  to  the  empty
              list  [].  A  link  is  created  between  the  calling process and the new process,
              atomically. Otherwise works like spawn/3.

       spawn_link(Node, Fun) -> pid()

              Types:

                 Node = node()
                 Fun = function()

              Returns the pid of a new process started by the application of  Fun  to  the  empty
              list [] on Node. A link is created between the calling process and the new process,
              atomically. If Node does not exist, a useless pid is returned (and due to the link,
              an  exit  signal  with  exit reason noconnection will be received). Otherwise works
              like spawn/3.

       spawn_link(Module, Function, Args) -> pid()

              Types:

                 Module = module()
                 Function = atom()
                 Args = [term()]

              Returns the pid of a new process started by the application of  Module:Function  to
              Args.  A  link  is  created  between  the  calling  process  and  the  new process,
              atomically. Otherwise works like spawn/3.

       spawn_link(Node, Module, Function, Args) -> pid()

              Types:

                 Node = node()
                 Module = module()
                 Function = atom()
                 Args = [term()]

              Returns the pid of a new process started by the application of  Module:Function  to
              Args  on  Node.  A link is created between the calling process and the new process,
              atomically. If Node does not exist, a useless pid is returned (and due to the link,
              an  exit  signal  with  exit reason noconnection will be received). Otherwise works
              like spawn/3.

       spawn_monitor(Fun) -> {pid(), reference()}

              Types:

                 Fun = function()

              Returns the pid of a new process started by the application of  Fun  to  the  empty
              list  []  and  reference  for a monitor created to the new process. Otherwise works
              like spawn/3.

       spawn_monitor(Module, Function, Args) -> {pid(), reference()}

              Types:

                 Module = module()
                 Function = atom()
                 Args = [term()]

              A new process is started by the application of Module:Function  to  Args,  and  the
              process  is  monitored  at  the  same time. Returns the pid and a reference for the
              monitor. Otherwise works like spawn/3.

       spawn_opt(Fun, Options) -> pid() | {pid(), reference()}

              Types:

                 Fun = function()
                 Options = [Option]
                 Option = link
                        | monitor
                        | {priority, Level :: priority_level()}
                        | {fullsweep_after, Number :: integer() >= 0}
                        | {min_heap_size, Size :: integer() >= 0}
                        | {min_bin_vheap_size, VSize :: integer() >= 0}
                 priority_level() = low | normal | high | max

              Returns the pid of a new process started by the application of  Fun  to  the  empty
              list []. Otherwise works like spawn_opt/4.

              If  the  option  monitor  is given, the newly created process will be monitored and
              both the pid and reference for the monitor will be returned.

       spawn_opt(Node, Fun, Options) -> pid() | {pid(), reference()}

              Types:

                 Node = node()
                 Fun = function()
                 Options = [Option]
                 Option = link
                        | monitor
                        | {priority, Level :: priority_level()}
                        | {fullsweep_after, Number :: integer() >= 0}
                        | {min_heap_size, Size :: integer() >= 0}
                        | {min_bin_vheap_size, VSize :: integer() >= 0}
                 priority_level() = low | normal | high | max

              Returns the pid of a new process started by the application of  Fun  to  the  empty
              list [] on Node. If Node does not exist, a useless pid is returned. Otherwise works
              like spawn_opt/4.

       spawn_opt(Module, Function, Args, Options) ->
                    pid() | {pid(), reference()}

              Types:

                 Module = module()
                 Function = atom()
                 Args = [term()]
                 Options = [Option]
                 Option = link
                        | monitor
                        | {priority, Level :: priority_level()}
                        | {fullsweep_after, Number :: integer() >= 0}
                        | {min_heap_size, Size :: integer() >= 0}
                        | {min_bin_vheap_size, VSize :: integer() >= 0}
                 priority_level() = low | normal | high | max

              Works exactly like spawn/3, except that an extra option list is given when creating
              the process.

              If  the  option  monitor  is given, the newly created process will be monitored and
              both the pid and reference for the monitor will be returned.

                link:
                  Sets a link to the parent process (like spawn_link/3 does).

                monitor:
                  Monitor the new process (just like monitor/2 does).

                {priority, Level}:
                  Sets   the   priority   of   the   new   process.   Equivalent   to   executing
                  process_flag(priority,  Level) in the start function of the new process, except
                  that the priority will be set before the process is selected for execution  for
                  the  first  time. For more information on priorities see process_flag(priority,
                  Level).

                {fullsweep_after, Number}:
                  This option is only useful for performance tuning. In general, you  should  not
                  use  this  option  unless  you  know that there is problem with execution times
                  and/or memory consumption, and you should measure to make sure that the  option
                  improved matters.

                  The  Erlang runtime system uses a generational garbage collection scheme, using
                  an "old heap" for data that has survived at least one garbage collection.  When
                  there  is  no more room on the old heap, a fullsweep garbage collection will be
                  done.

                  The fullsweep_after option makes it possible to specify the maximum  number  of
                  generational collections before forcing a fullsweep even if there is still room
                  on the old heap. Setting the number to zero effectively  disables  the  general
                  collection  algorithm,  meaning  that  all live data is copied at every garbage
                  collection.

                  Here are a few cases  when  it  could  be  useful  to  change  fullsweep_after.
                  Firstly,  if  binaries that are no longer used should be thrown away as soon as
                  possible. (Set Number to zero.) Secondly, a process  that  mostly  have  short-
                  lived  data will be fullsweeped seldom or never, meaning that the old heap will
                  contain mostly garbage. To ensure a fullsweep once in a while, set Number to  a
                  suitable  value  such  as  10  or 20. Thirdly, in embedded systems with limited
                  amount of RAM and no virtual memory, one  might  want  to  preserve  memory  by
                  setting   Number   to   zero.   (The   value   may   be   set   globally,   see
                  erlang:system_flag/2.)

                {min_heap_size, Size}:
                  This option is only useful for performance tuning. In general, you  should  not
                  use  this  option  unless  you  know that there is problem with execution times
                  and/or memory consumption, and you should measure to make sure that the  option
                  improved matters.

                  Gives  a  minimum heap size in words. Setting this value higher than the system
                  default might speed up some processes because less garbage collection is  done.
                  Setting  too  high  value, however, might waste memory and slow down the system
                  due to worse data locality. Therefore, it is recommended  to  use  this  option
                  only  for  fine-tuning  an  application  and to measure the execution time with
                  various Size values.

                {min_bin_vheap_size, VSize}:
                  This option is only useful for performance tuning. In general, you  should  not
                  use  this  option  unless  you  know that there is problem with execution times
                  and/or memory consumption, and you should measure to make sure that the  option
                  improved matters.

                  Gives  a  minimum  binary virtual heap size in words. Setting this value higher
                  than the system default might speed up  some  processes  because  less  garbage
                  collection  is  done.  Setting  too  high  value,  however, might waste memory.
                  Therefore, it is recommended  to  use  this  option  only  for  fine-tuning  an
                  application and to measure the execution time with various VSize values.

       spawn_opt(Node, Module, Function, Args, Options) ->
                    pid() | {pid(), reference()}

              Types:

                 Node = node()
                 Module = module()
                 Function = atom()
                 Args = [term()]
                 Options = [Option]
                 Option = link
                        | monitor
                        | {priority, Level :: priority_level()}
                        | {fullsweep_after, Number :: integer() >= 0}
                        | {min_heap_size, Size :: integer() >= 0}
                        | {min_bin_vheap_size, VSize :: integer() >= 0}
                 priority_level() = low | normal | high | max

              Returns  the  pid of a new process started by the application of Module:Function to
              Args on Node. If Node does not exist, a useless pid is  returned.  Otherwise  works
              like spawn_opt/4.

       split_binary(Bin, Pos) -> {binary(), binary()}

              Types:

                 Bin = binary()
                 Pos = integer() >= 0
                   0..byte_size(Bin)

              Returns  a tuple containing the binaries which are the result of splitting Bin into
              two parts at  position  Pos.  This  is  not  a  destructive  operation.  After  the
              operation, there will be three binaries altogether.

              > B = list_to_binary("0123456789").
              <<"0123456789">>
              > byte_size(B).
              10
              > {B1, B2} = split_binary(B,3).
              {<<"012">>,<<"3456789">>}
              > byte_size(B1).
              3
              > byte_size(B2).
              7

       erlang:start_timer(Time, Dest, Msg) -> TimerRef

              Types:

                 Time = integer() >= 0
                   0 <= Time <= 4294967295
                 Dest = pid() | atom()
                 Msg = term()
                 TimerRef = reference()

              Starts  a  timer which will send the message {timeout, TimerRef, Msg} to Dest after
              Time milliseconds.

              If Dest is a pid() it has to be a pid() of a local process, dead or alive.

              The Time value can, in the current implementation, not be greater than 4294967295.

              If Dest is an atom(), it is supposed to be the name of a  registered  process.  The
              process  referred  to by the name is looked up at the time of delivery. No error is
              given if the name does not refer to a process.

              If Dest is a pid(), the  timer  will  be  automatically  canceled  if  the  process
              referred  to by the pid() is not alive, or when the process exits. This feature was
              introduced in erts version 5.4.11. Note  that  timers  will  not  be  automatically
              canceled when Dest is an atom().

              See also erlang:send_after/3, erlang:cancel_timer/1, and erlang:read_timer/1.

              Failure: badarg if the arguments does not satisfy the requirements specified above.

       statistics(Item :: context_switches) -> {ContextSwitches, 0}

              Types:

                 ContextSwitches = integer() >= 0

              ContextSwitches is the total number of context switches since the system started.

       statistics(Item :: exact_reductions) ->
                     {Total_Exact_Reductions,
                      Exact_Reductions_Since_Last_Call}

              Types:

                 Total_Exact_Reductions = Exact_Reductions_Since_Last_Call = integer() >= 0

          Note:
              statistics(exact_reductions)     is     a    more    expensive    operation    than
              statistics(reductions) especially on an Erlang machine with SMP support.

       statistics(Item :: garbage_collection) ->
                     {Number_of_GCs, Words_Reclaimed, 0}

              Types:

                 Number_of_GCs = Words_Reclaimed = integer() >= 0

              This information may not be valid for all implementations.

              > statistics(garbage_collection).
              {85,23961,0}

       statistics(Item :: io) -> {{input, Input}, {output, Output}}

              Types:

                 Input = Output = integer() >= 0

              Input is the total number of bytes received through ports, and Output is the  total
              number of bytes output to ports.

       statistics(Item :: reductions) ->
                     {Total_Reductions, Reductions_Since_Last_Call}

              Types:

                 Total_Reductions = Reductions_Since_Last_Call = integer() >= 0

          Note:
              Since  erts-5.5 (OTP release R11B) this value does not include reductions performed
              in current time slices of currently scheduled  processes.  If  an  exact  value  is
              wanted, use statistics(exact_reductions).

              > statistics(reductions).
              {2046,11}

       statistics(Item :: run_queue) -> integer() >= 0

              Returns  the  total length of the run queues, that is, the number of processes that
              are ready to run on all available run queues.

       statistics(Item :: runtime) ->
                     {Total_Run_Time, Time_Since_Last_Call}

              Types:

                 Total_Run_Time = Time_Since_Last_Call = integer() >= 0

              Note that the run-time is the sum of the run-time for all  threads  in  the  Erlang
              run-time system and may therefore be greater than the wall-clock time.

              > statistics(runtime).
              {1690,1620}

       statistics(Item :: scheduler_wall_time) ->
                     [{SchedulerId, ActiveTime, TotalTime}] | undefined

              Types:

                 SchedulerId = integer() >= 1
                 ActiveTime = TotalTime = integer() >= 0

              Returns   a  list  of  tuples  with  {SchedulerId,  ActiveTime,  TotalTime},  where
              SchedulerId is an integer id of the  scheduler,  ActiveTime  is  the  duration  the
              scheduler   has   been   busy,   TotalTime   is   the  total  time  duration  since
              scheduler_wall_time activation. The time unit is not defined and may be subject  to
              change between releases, operating systems and system restarts. scheduler_wall_time
              should only  be  used  to  calculate  relative  values  for  scheduler-utilization.
              ActiveTime can never exceed TotalTime.

              The  definition  of  a  busy  scheduler  is  when  it is not idle or not scheduling
              (selecting) a process or port, meaning; executing process code,  executing  linked-
              in-driver  or NIF code, executing built-in-functions or any other runtime handling,
              garbage collecting or handling any other memory management. Note, a  scheduler  may
              also be busy even if the operating system has scheduled out the scheduler thread.

              Returns undefined if the system flag scheduler_wall_time is turned off.

              The  list  of  scheduler  information is unsorted and may appear in different order
              between calls.

              Using scheduler_wall_time to calculate scheduler utilization.

              > erlang:system_flag(scheduler_wall_time, true).
              false
              > Ts0 = lists:sort(erlang:statistics(scheduler_wall_time)), ok.
              ok

              Some time later we will take another snapshot and  calculate  scheduler-utilization
              per scheduler.

              > Ts1 = lists:sort(erlang:statistics(scheduler_wall_time)), ok.
              ok
              > lists:map(fun({{I, A0, T0}, {I, A1, T1}}) -> {I, (A1 - A0)/(T1 - T0)} end, lists:zip(Ts0,Ts1)).
              [{1,0.9743474730177548},
               {2,0.9744843782751444},
               {3,0.9995902361669045},
               {4,0.9738012596572161},
               {5,0.9717956667018103},
               {6,0.9739235846420741},
               {7,0.973237033077876},
               {8,0.9741297293248656}]

              Using the same snapshots to calculate a total scheduler-utilization.

              > {A, T} = lists:foldl(fun({{_, A0, T0}, {_, A1, T1}}, {Ai,Ti}) -> {Ai + (A1 - A0), Ti + (T1 - T0)} end, {0, 0}, lists:zip(Ts0,Ts1)), A/T.
              0.9769136803764825

          Note:
              scheduler_wall_time         is        by        default        disabled.        Use
              erlang:system_flag(scheduler_wall_time, true) to enable it.

       statistics(Item :: wall_clock) ->
                     {Total_Wallclock_Time,
                      Wallclock_Time_Since_Last_Call}

              Types:

                 Total_Wallclock_Time = Wallclock_Time_Since_Last_Call = integer() >= 0

              wall_clock can be used in the same manner as runtime,  except  that  real  time  is
              measured as opposed to runtime or CPU time.

       erlang:suspend_process(Suspendee, OptList) -> boolean()

              Types:

                 Suspendee = pid()
                 OptList = [Opt]
                 Opt = unless_suspending | asynchronous

              Increases  the  suspend count on the process identified by Suspendee and puts it in
              the suspended state if it isn't already in the suspended state. A suspended process
              will not be scheduled for execution until the process has been resumed.

              A  process  can  be  suspended  by multiple processes and can be suspended multiple
              times by a single process. A suspended process will not leave the  suspended  state
              until  its  suspend  count  reach zero. The suspend count of Suspendee is decreased
              when erlang:resume_process(Suspendee) is called by the  same  process  that  called
              erlang:suspend_process(Suspendee).  All increased suspend counts on other processes
              acquired by a process will automatically be decreased when the process terminates.

              Currently the following options (Opts) are available:

                asynchronous:
                   A suspend request is sent to the process identified  by  Suspendee.  Suspendee
                  will eventually suspend unless it is resumed before it was able to suspend. The
                  caller of  erlang:suspend_process/2  will  return  immediately,  regardless  of
                  whether  the  Suspendee  has  suspended yet or not. Note that the point in time
                  when the Suspendee will actually suspend cannot be deduced from other events in
                  the  system.  The  only  guarantee  given is that the Suspendee will eventually
                  suspend (unless it is resumed). If the asynchronous option has not been passed,
                  the  caller of erlang:suspend_process/2 will be blocked until the Suspendee has
                  actually suspended.

                unless_suspending:
                   The process identified by Suspendee  will  be  suspended  unless  the  calling
                  process  already  is suspending the Suspendee. If unless_suspending is combined
                  with the asynchronous option, a suspend request will be sent unless the calling
                  process already is suspending the Suspendee or if a suspend request already has
                  been sent and is in transit. If the calling process already is  suspending  the
                  Suspendee,  or  if  combined  with  the  asynchronous option and a send request
                  already is in transit, false is returned and the  suspend  count  on  Suspendee
                  will remain unchanged.

              If  the suspend count on the process identified by Suspendee was increased, true is
              returned; otherwise, false is returned.

          Warning:
              This BIF is intended for debugging only.

              Failures:

                badarg:
                   If Suspendee isn't a process identifier.

                badarg:
                   If the process identified by Suspendee is same  the  process  as  the  process
                  calling erlang:suspend_process/2.

                badarg:
                   If the process identified by Suspendee is not alive.

                badarg:
                   If the process identified by Suspendee resides on another node.

                badarg:
                   If OptList isn't a proper list of valid Opts.

                system_limit:
                   If  the  process  identified by Suspendee has been suspended more times by the
                  calling process than can be represented by the  currently  used  internal  data
                  structures. The current system limit is larger than 2 000 000 000 suspends, and
                  it will never be less than that.

       erlang:suspend_process(Suspendee) -> true

              Types:

                 Suspendee = pid()

              Suspends   the   process   identified   by   Suspendee.   The   same   as   calling
              erlang:suspend_process(Suspendee,  []).  For more information see the documentation
              of erlang:suspend_process/2.

          Warning:
              This BIF is intended for debugging only.

       erlang:system_flag(Flag :: backtrace_depth, Depth) -> OldDepth

              Types:

                 Depth = OldDepth = integer() >= 0

              Sets the maximum depth of call stack back-traces in  the  exit  reason  element  of
              'EXIT' tuples.

              Returns the old value of the flag.

       erlang:system_flag(Flag :: cpu_topology, CpuTopology) ->
                             OldCpuTopology

              Types:

                 CpuTopology = OldCpuTopology = cpu_topology()
                 cpu_topology() = [LevelEntry :: level_entry()] | undefined
                 level_entry() = {LevelTag :: level_tag(),
                                  SubLevel :: sub_level()}
                               | {LevelTag :: level_tag(),
                                  InfoList :: info_list(),
                                  SubLevel :: sub_level()}
                 level_tag() = core | node | processor | thread
                 sub_level() = [LevelEntry :: level_entry()]
                             | (LogicalCpuId :: {logical, integer() >= 0})
                 info_list() = []

          Warning:
              This argument is deprecated and scheduled for removal in erts-5.10/OTP-R16. Instead
              of using this argument you are advised to use the erl command line  argument  +sct.
              When  this argument has been removed a final CPU topology to use will be determined
              at emulator boot time.

              Sets the user defined CpuTopology. The user defined CPU topology will override  any
              automatically detected CPU topology. By passing undefined as CpuTopology the system
              will revert back to the CPU topology automatically  detected.  The  returned  value
              equals  the  value returned from erlang:system_info(cpu_topology) before the change
              was made.

              Returns the old value of the flag.

              The CPU topology  is  used  when  binding  schedulers  to  logical  processors.  If
              schedulers  are already bound when the CPU topology is changed, the schedulers will
              be sent a request to rebind according to the new CPU topology.

              The user defined CPU topology can also be set by  passing  the  +sct  command  line
              argument to erl.

              For  information  on  the  CpuTopology  type  and  more,  see  the documentation of
              erlang:system_info(cpu_topology), and the erl +sct and +sbt command line flags.

       erlang:system_flag(Flag :: fullsweep_after, Number) -> OldNumber

              Types:

                 Number = OldNumber = integer() >= 0

              Number is a non-negative  integer  which  indicates  how  many  times  generational
              garbage  collections  can be done without forcing a fullsweep collection. The value
              applies to new processes; processes already running are not affected.

              Returns the old value of the flag.

              In low-memory systems (especially without virtual memory), setting the value  to  0
              can help to conserve memory.

              An  alternative way to set this value is through the (operating system) environment
              variable ERL_FULLSWEEP_AFTER.

       erlang:system_flag(Flag :: min_heap_size, MinHeapSize) ->
                             OldMinHeapSize

              Types:

                 MinHeapSize = OldMinHeapSize = integer() >= 0

              Sets the default minimum heap size for processes. The size is given in  words.  The
              new  min_heap_size only effects processes spawned after the change of min_heap_size
              has been made. The min_heap_size can be set for  individual  processes  by  use  of
              spawn_opt/N or process_flag/2.

              Returns the old value of the flag.

       erlang:system_flag(Flag :: min_bin_vheap_size, MinBinVHeapSize) ->
                             OldMinBinVHeapSize

              Types:

                 MinBinVHeapSize = OldMinBinVHeapSize = integer() >= 0

              Sets  the default minimum binary virtual heap size for processes. The size is given
              in words. The new min_bin_vhheap_size only  effects  processes  spawned  after  the
              change  of min_bin_vhheap_size has been made. The min_bin_vheap_size can be set for
              individual processes by use of spawn_opt/N or process_flag/2.

              Returns the old value of the flag.

       erlang:system_flag(Flag :: multi_scheduling, BlockState) ->
                             OldBlockState

              Types:

                 BlockState = block | unblock
                 OldBlockState = block | unblock | enabled

              If multi-scheduling is enabled, more than one  scheduler  thread  is  used  by  the
              emulator.  Multi-scheduling can be blocked. When multi-scheduling has been blocked,
              only one scheduler thread will schedule Erlang processes.

              If BlockState =:= block,  multi-scheduling  will  be  blocked.  If  BlockState  =:=
              unblock  and  no-one  else  is  blocking multi-scheduling and this process has only
              blocked one time, multi-scheduling will be unblocked. One process can block  multi-
              scheduling  multiple  times.  If  a  process  has blocked multiple times, it has to
              unblock exactly as many times as it has blocked before it has released  its  multi-
              scheduling  block.  If  a  process that has blocked multi-scheduling exits, it will
              release its blocking of multi-scheduling.

              The return values are disabled, blocked, or enabled. The returned  value  describes
              the  state  just after the call to erlang:system_flag(multi_scheduling, BlockState)
              has  been  made.  The  return  values  are  described  in  the   documentation   of
              erlang:system_info(multi_scheduling).

              NOTE:  Blocking of multi-scheduling should normally not be needed. If you feel that
              you need to block multi-scheduling, think through the problem at least a couple  of
              times  again.  Blocking multi-scheduling should only be used as a last resort since
              it will most likely be a very inefficient way to solve the problem.

              See                   also                    erlang:system_info(multi_scheduling),
              erlang:system_info(multi_scheduling_blockers), and erlang:system_info(schedulers).

       erlang:system_flag(Flag :: scheduler_bind_type, How) ->
                             OldBindType

              Types:

                 How = scheduler_bind_type() | default_bind
                 OldBindType = scheduler_bind_type()
                 scheduler_bind_type() = no_node_processor_spread
                                       | no_node_thread_spread
                                       | no_spread
                                       | processor_spread
                                       | spread
                                       | thread_spread
                                       | thread_no_node_processor_spread
                                       | unbound

          Warning:
              This argument is deprecated and scheduled for removal in erts-5.10/OTP-R16. Instead
              of using this argument you are advised to use the erl command line  argument  +sbt.
              When  this  argument  has  been  removed a final scheduler bind type to use will be
              determined at emulator boot time.

              Controls if and how schedulers are bound to logical processors.

              When erlang:system_flag(scheduler_bind_type, How) is called, an asynchronous signal
              is  sent  to  all  schedulers  online which causes them to try to bind or unbind as
              requested. NOTE: If a scheduler fails to bind, this will often be silently ignored.
              This  since it isn't always possible to verify valid logical processor identifiers.
              If an error is reported, it will be reported to the error_logger. If  you  want  to
              verify   that   the   schedulers   actually   have   bound   as   requested,   call
              erlang:system_info(scheduler_bindings).

              Schedulers can currently only be  bound  on  newer  Linux,  Solaris,  FreeBSD,  and
              Windows systems, but more systems will be supported in the future.

              In  order  for  the  runtime system to be able to bind schedulers, the CPU topology
              needs to be known. If the runtime system fails  to  automatically  detect  the  CPU
              topology,  it  can  be  defined.  For  more  information  on  how to define the CPU
              topology, see the erl +sct command line flag.

              The runtime system will by default not bind schedulers to logical processors.

              NOTE: If the Erlang runtime system is the only operating system process that  binds
              threads to logical processors, this improves the performance of the runtime system.
              However, if other operating system processes (as for example another Erlang runtime
              system)  also  bind  threads  to  logical  processors, there might be a performance
              penalty instead. In some cases this performance penalty might be severe. If this is
              the case, you are advised to not bind the schedulers.

              Schedulers  can  be  bound  in  different  ways.  The  How  argument determines how
              schedulers are bound. How can currently be one of:

                unbound:
                  Same as the erl command line argument +sbt u.

                no_spread:
                  Same as the erl command line argument +sbt ns.

                thread_spread:
                  Same as the erl command line argument +sbt ts.

                processor_spread:
                  Same as the erl command line argument +sbt ps.

                spread:
                  Same as the erl command line argument +sbt s.

                no_node_thread_spread:
                  Same as the erl command line argument +sbt nnts.

                no_node_processor_spread:
                  Same as the erl command line argument +sbt nnps.

                thread_no_node_processor_spread:
                  Same as the erl command line argument +sbt tnnps.

                default_bind:
                  Same as the erl command line argument +sbt db.

              The value returned equals How before the scheduler_bind_type flag was changed.

              Failure:

                notsup:
                  If binding of schedulers is not supported.

                badarg:
                  If How isn't one of the documented alternatives.

                badarg:
                  If no CPU topology information is available.

              The scheduler bind type can also be set by passing the +sbt command  line  argument
              to erl.

              For      more     information,     see     erlang:system_info(scheduler_bind_type),
              erlang:system_info(scheduler_bindings), the erl +sbt and +sct command line flags.

       erlang:system_flag(Flag :: scheduler_wall_time, Boolean) ->
                             OldBoolean

              Types:

                 Boolean = OldBoolean = boolean()

              Turns on/off scheduler wall time measurements.

              For more information see, erlang:statistics(scheduler_wall_time).

       erlang:system_flag(Flag :: schedulers_online, SchedulersOnline) ->
                             OldSchedulersOnline

              Types:

                 SchedulersOnline = OldSchedulersOnline = integer() >= 1

              Sets the amount of schedulers online. Valid  range  is  1  <=  SchedulersOnline  <=
              erlang:system_info(schedulers).

              Returns the old value of the flag.

              For      more      information     see,     erlang:system_info(schedulers),     and
              erlang:system_info(schedulers_online).

       erlang:system_flag(Flag :: trace_control_word, TCW) -> OldTCW

              Types:

                 TCW = OldTCW = integer() >= 0

              Sets the value of the node's trace control word to TCW. TCW should be  an  unsigned
              integer.  For  more  information  see  documentation of the set_tcw function in the
              match specification documentation in the ERTS User's Guide.

              Returns the old value of the flag.

       erlang:system_info(Item :: allocated_areas) -> [tuple()]

       erlang:system_info(Item :: allocator) ->
                             {Allocator, Version, Features, Settings}

       erlang:system_info(Item :: alloc_util_allocators) -> [Alloc]

       erlang:system_info(Item :: {allocator, Alloc}) -> [term()]

       erlang:system_info(Item :: {allocator_sizes, Alloc}) -> [term()]

              Types:

                 Allocator = undefined | glibc
                 Version = [integer() >= 0]
                 Features = [atom()]
                 Settings =
                     [{Subsystem :: atom(),
                       [{Parameter :: atom(), Value :: term()}]}]
                 Alloc = atom()

              Returns various information about the allocators of the current  system  (emulator)
              as specified by Item:

                allocated_areas:
                  Returns  a list of tuples with information about miscellaneous allocated memory
                  areas.

                  Each tuple contains an atom describing type of  memory  as  first  element  and
                  amount  of  allocated  memory  in  bytes as second element. In those cases when
                  there is information present about allocated and used memory, a  third  element
                  is present. This third element contains the amount of used memory in bytes.

                  erlang:system_info(allocated_areas)  is intended for debugging, and the content
                  is highly implementation dependent. The content of the results  will  therefore
                  change when needed without prior notice.

                  Note:  The  sum  of these values is not the total amount of memory allocated by
                  the emulator. Some values are part of other values, and some memory  areas  are
                  not  part  of  the  result. If you are interested in the total amount of memory
                  allocated by the emulator see erlang:memory/0,1.

                allocator:
                  Returns {Allocator, Version, Features, Settings}.

                  Explanation:

                  * Allocator corresponds to  the  malloc()  implementation  used.  If  Allocator
                    equals  undefined,  the malloc() implementation used could not be identified.
                    Currently glibc can be identified.

                  * Version is a list of integers (but not a string) representing the version  of
                    the malloc() implementation used.

                  * Features is a list of atoms representing allocation features used.

                  * Settings  is  a  list  of subsystems, their configurable parameters, and used
                    values. Settings may differ  between  different  combinations  of  platforms,
                    allocators, and allocation features. Memory sizes are given in bytes.

                  See also "System Flags Effecting erts_alloc" in erts_alloc(3erl).

                alloc_util_allocators:
                  Returns  a  list  of  the  names  of  all  allocators  using  the ERTS internal
                  alloc_util framework as atoms. For more information  see  the  "the  alloc_util
                  framework" section in the erts_alloc(3erl) documentation.

                {allocator, Alloc}:
                  Returns information about the specified allocator. As of erts version 5.6.1 the
                  return value is a list of {instance,  InstanceNo,  InstanceInfo}  tuples  where
                  InstanceInfo  contains  information about a specific instance of the allocator.
                  As   of   erts   version   5.10.4    the    returned    list    when    calling
                  erlang:system_info({allocator,  mseg_alloc})  also  include  an  {erts_mmap, _}
                  tuple as one element in the list. If  Alloc  is  not  a  recognized  allocator,
                  undefined is returned. If Alloc is disabled, false is returned.

                  Note:  The  information  returned is highly implementation dependent and may be
                  changed, or removed at any time without prior notice. It was initially intended
                  as a tool when developing new allocators, but since it might be of interest for
                  others it has been briefly documented.

                  The recognized allocators are listed in  erts_alloc(3erl).  After  reading  the
                  erts_alloc(3erl)  documentation,  the  returned information should more or less
                  speak for itself. But it can be worth explaining some things. Call  counts  are
                  presented by two values. The first value is giga calls, and the second value is
                  calls.  mbcs,  and  sbcs  are  abbreviations  for,  respectively,   multi-block
                  carriers,  and  single-block carriers. Sizes are presented in bytes. When it is
                  not a size that is presented, it is the amount of something. Sizes and  amounts
                  are  often presented by three values, the first is current value, the second is
                  maximum value since the last call  to  erlang:system_info({allocator,  Alloc}),
                  and  the  third  is  maximum  value since the emulator was started. If only one
                  value is present, it is the current value. fix_alloc  memory  block  types  are
                  presented  by  two  values.  The first value is memory pool size and the second
                  value used memory size.

                {allocator_sizes, Alloc}:
                  Returns various size information for the specified allocator.  The  information
                  returned     is     a     subset     of    the    information    returned    by
                  erlang:system_info({allocator, Alloc}).

       erlang:system_info(Item :: cpu_topology) -> CpuTopology

       erlang:system_info(Item ::
                              {cpu_topology, defined | detected | used}) ->
                             CpuTopology

              Types:

                 CpuTopology = cpu_topology()
                 cpu_topology() = [LevelEntry :: level_entry()] | undefined
                    All LevelEntrys of a list must contain the same LevelTag, except on  the  top
                   level where both node and processorLevelTags may co-exist.
                 level_entry() = {LevelTag :: level_tag(),
                                  SubLevel :: sub_level()}
                               | {LevelTag :: level_tag(),
                                  InfoList :: info_list(),
                                  SubLevel :: sub_level()}
                   {LevelTag, SubLevel} == {LevelTag, [], SubLevel}
                 level_tag() = core | node | processor | thread
                    More LevelTags may be introduced in the future.
                 sub_level() = [LevelEntry :: level_entry()]
                             | (LogicalCpuId :: {logical, integer() >= 0})
                 info_list() = []
                    The info_list() may be extended in the future.

              Returns various information about the CPU topology of the current system (emulator)
              as specified by Item:

                cpu_topology:
                  Returns the CpuTopology which currently  is  used  by  the  emulator.  The  CPU
                  topology  is  used  when  binding  schedulers  to  logical  processors. The CPU
                  topology used is the user defined CPU topology if such exists;  otherwise,  the
                  automatically  detected CPU topology if such exists. If no CPU topology exists,
                  undefined is returned.

                  node refers to NUMA (non-uniform memory access) nodes,  and  thread  refers  to
                  hardware threads (e.g. Intels hyper-threads).

                  A level in the CpuTopology term can be omitted if only one entry exists and the
                  InfoList is empty.

                  thread can only be a sub level to core. core can  be  a  sub  level  to  either
                  processor  or  node. processor can either be on the top level or a sub level to
                  node. node can either be on the top level or a sub level to processor. That is,
                  NUMA  nodes can be processor internal or processor external. A CPU topology can
                  consist of a mix of processor internal and external NUMA nodes, as long as each
                  logical  CPU belongs to one and only one NUMA node. Cache hierarchy is not part
                  of the CpuTopology type yet, but will be in the future. Other things  may  also
                  make  it  into  the  CPU  topology  in  the  future. In other words, expect the
                  CpuTopology type to change.

                {cpu_topology, defined}:
                  Returns  the  user  defined  CpuTopology.  For   more   information   see   the
                  documentation  of  the erl +sct command line flag, and the documentation of the
                  cpu_topology argument.

                {cpu_topology, detected}:
                  Returns the automatically detected CpuTopology.  The  emulator  currently  only
                  detects  the  CPU  topology  on some newer Linux, Solaris, FreeBSD, and Windows
                  systems. On Windows system  with  more  than  32  logical  processors  the  CPU
                  topology is not detected.

                  For more information see the documentation of the cpu_topology argument.

                {cpu_topology, used}:
                  Returns the CpuTopology which is used by the emulator. For more information see
                  the documentation of the cpu_topology argument.

       erlang:system_info(Item :: build_type) ->
                             opt |
                             debug |
                             purify |
                             quantify |
                             purecov |
                             gcov |
                             valgrind |
                             gprof |
                             lcnt |
                             frmptr

       erlang:system_info(Item :: c_compiler_used) -> {atom(), term()}

       erlang:system_info(Item :: check_io) -> [term()]

       erlang:system_info(Item :: compat_rel) -> integer()

       erlang:system_info(Item :: creation) -> integer()

       erlang:system_info(Item :: debug_compiled) -> boolean()

       erlang:system_info(Item :: dist) -> binary()

       erlang:system_info(Item :: dist_buf_busy_limit) ->
                             integer() >= 0

       erlang:system_info(Item :: dist_ctrl) ->
                             {Node :: node(),
                              ControllingEntity :: port() | pid()}

       erlang:system_info(Item :: driver_version) -> string()

       erlang:system_info(Item :: dynamic_trace) ->
                             none | dtrace | systemtap

       erlang:system_info(Item :: dynamic_trace_probes) -> boolean()

       erlang:system_info(Item :: elib_malloc) -> false

       erlang:system_info(Item :: ets_limit) -> integer() >= 1

       erlang:system_info(Item :: fullsweep_after) ->
                             {fullsweep_after, integer() >= 0}

       erlang:system_info(Item :: garbage_collection) ->
                             [{atom(), integer()}]

       erlang:system_info(Item :: heap_sizes) -> [integer() >= 0]

       erlang:system_info(Item :: heap_type) -> private

       erlang:system_info(Item :: info) -> binary()

       erlang:system_info(Item :: kernel_poll) -> boolean()

       erlang:system_info(Item :: loaded) -> binary()

       erlang:system_info(Item :: logical_processors
                                | logical_processors_available
                                | logical_processors_online) ->
                             unknown | integer() >= 1

       erlang:system_info(Item :: machine) -> string()

       erlang:system_info(Item :: min_heap_size) ->
                             {min_heap_size,
                              MinHeapSize :: integer() >= 1}

       erlang:system_info(Item :: min_bin_vheap_size) ->
                             {min_bin_vheap_size,
                              MinBinVHeapSize :: integer() >= 1}

       erlang:system_info(Item :: modified_timing_level) ->
                             integer() | undefined

       erlang:system_info(Item :: multi_scheduling) ->
                             disabled | blocked | enabled

       erlang:system_info(Item :: multi_scheduling_blockers) ->
                             [PID :: pid()]

       erlang:system_info(Item :: otp_release) -> string()

       erlang:system_info(Item :: port_count) -> integer() >= 0

       erlang:system_info(Item :: port_limit) -> integer() >= 1

       erlang:system_info(Item :: process_count) -> integer() >= 1

       erlang:system_info(Item :: process_limit) -> integer() >= 1

       erlang:system_info(Item :: procs) -> binary()

       erlang:system_info(Item :: scheduler_bind_type) ->
                             spread |
                             processor_spread |
                             thread_spread |
                             thread_no_node_processor_spread |
                             no_node_processor_spread |
                             no_node_thread_spread |
                             no_spread |
                             unbound

       erlang:system_info(Item :: scheduler_bindings) -> tuple()

       erlang:system_info(Item :: scheduler_id) ->
                             SchedulerId :: integer() >= 1

       erlang:system_info(Item :: schedulers | schedulers_online) ->
                             integer() >= 1

       erlang:system_info(Item :: smp_support) -> boolean()

       erlang:system_info(Item :: system_version) -> string()

       erlang:system_info(Item :: system_architecture) -> string()

       erlang:system_info(Item :: threads) -> boolean()

       erlang:system_info(Item :: thread_pool_size) -> integer() >= 0

       erlang:system_info(Item :: trace_control_word) ->
                             integer() >= 0

       erlang:system_info(Item :: update_cpu_info) -> changed | unchanged

       erlang:system_info(Item :: version) -> string()

       erlang:system_info(Item :: wordsize
                                | {wordsize, internal}
                                | {wordsize, external}) ->
                             4 | 8

              Returns various information about the current system  (emulator)  as  specified  by
              Item:

                allocated_areas, allocator, alloc_util_allocators, allocator_sizes:
                  See above.

                build_type:
                  Returns  an  atom  describing  the  build  type  of the runtime system. This is
                  normally the atom opt for optimized. Other possible return  values  are  debug,
                  purify,  quantify,  purecov,  gcov,  valgrind, gprof, and lcnt. Possible return
                  values may be added and/or removed at any time without prior notice.

                c_compiler_used:
                  Returns a two-tuple describing the C compiler used when compiling  the  runtime
                  system.  The  first  element is an atom describing the name of the compiler, or
                  undefined if unknown. The second element is a term describing  the  version  of
                  the compiler, or undefined if unknown.

                check_io:
                  Returns  a  list  containing  miscellaneous information regarding the emulators
                  internal I/O checking. Note, the content of the returned list may vary  between
                  platforms and over time. The only thing guaranteed is that a list is returned.

                compat_rel:
                  Returns  the  compatibility  mode  of the local node as an integer. The integer
                  returned represents the Erlang/OTP release which the current emulator has  been
                  set to be backward compatible with. The compatibility mode can be configured at
                  startup by using the command line flag +R, see erl(1).

                cpu_topology:
                  See above.

                creation:
                  Returns the creation of the local node as an integer. The creation  is  changed
                  when  a  node  is  restarted.  The  creation  of  a  node  is stored in process
                  identifiers, port identifiers, and references. This makes it (to  some  extent)
                  possible  to  distinguish  between identifiers from different incarnations of a
                  node. Currently valid creations are integers in the range 1..3,  but  this  may
                  (probably will) change in the future. If the node is not alive, 0 is returned.

                debug_compiled:
                  Returns true if the emulator has been debug compiled; otherwise, false.

                dist:
                  Returns  a  binary containing a string of distribution information formatted as
                  in Erlang crash dumps. For more information  see  the  "How  to  interpret  the
                  Erlang crash dumps" chapter in the ERTS User's Guide.

                dist_buf_busy_limit:
                  Returns  the  value  of the distribution buffer busy limit in bytes. This limit
                  can be set on startup by passing the +zdbbl command line flag to erl.

                dist_ctrl:
                  Returns a  list  of  tuples  {Node,  ControllingEntity},  one  entry  for  each
                  connected   remote   node.   The   Node  is  the  name  of  the  node  and  the
                  ControllingEntity is the port or pid responsible for the communication to  that
                  node.  More  specifically, the ControllingEntity for nodes connected via TCP/IP
                  (the normal case) is  the  socket  actually  used  in  communication  with  the
                  specific node.

                driver_version:
                  Returns  a  string  containing  the  erlang  driver version used by the runtime
                  system. It will be on the form "<major ver>.<minor ver>".

                dynamic_trace:
                  Returns an atom describing  the  dynamic  trace  framework  compiled  into  the
                  virtual  machine.  It  can currently be either dtrace, systemtap or none. For a
                  commercial or standard build, this is always  none,  the  other  return  values
                  indicate a custom configuration (e.g. ./configure --with-dynamic-trace=dtrace).
                  See the dyntrace  manual page and the README.dtrace/README.systemtap  files  in
                  the  Erlang  source  code  top  directory  for  more  information about dynamic
                  tracing.

                dynamic_trace_probes:
                  Returns a boolean() indicating  if  dynamic  trace  probes  (either  dtrace  or
                  systemtap)  are  built  into the emulator. This can only be true if the virtual
                  machine was built for dynamic tracing (i.e. system_info(dynamic_trace)  returns
                  dtrace or systemtap).

                elib_malloc:
                  This  option  will be removed in a future release. The return value will always
                  be false since the elib_malloc allocator has been removed.

                ets_limit:
                  Returns the maximum number of ETS tables allowed. This limit can  be  increased
                  on  startup  by  passing  the  +e  command  line  flag to erl or by setting the
                  environment variable ERL_MAX_ETS_TABLES  before  starting  the  Erlang  runtime
                  system.

                fullsweep_after:
                  Returns  {fullsweep_after, integer() >= 0} which is the fullsweep_after garbage
                  collection setting used by default. For more information see garbage_collection
                  described below.

                garbage_collection:
                  Returns  a  list  describing the default garbage collection settings. A process
                  spawned on the local node by a spawn  or  spawn_link  will  use  these  garbage
                  collection   settings.   The   default  settings  can  be  changed  by  use  of
                  system_flag/2. spawn_opt/4 can spawn a process that does not  use  the  default
                  settings.

                heap_sizes:
                  Returns  a  list of integers representing valid heap sizes in words. All Erlang
                  heaps are sized from sizes in this list.

                heap_type:
                  Returns the heap  type  used  by  the  current  emulator.  Currently  only  the
                  following heap type exists:

                  private:
                    Each  process has a heap reserved for its use and no references between heaps
                    of different processes are allowed. Messages  passed  between  processes  are
                    copied between heaps.

                info:
                  Returns  a  binary  containing  a  string  of  miscellaneous system information
                  formatted as in Erlang crash dumps.  For  more  information  see  the  "How  to
                  interpret the Erlang crash dumps" chapter in the ERTS User's Guide.

                kernel_poll:
                  Returns  true  if  the  emulator  uses some kind of kernel-poll implementation;
                  otherwise, false.

                loaded:
                  Returns a binary containing a string of loaded module information formatted  as
                  in  Erlang  crash  dumps.  For  more  information see the "How to interpret the
                  Erlang crash dumps" chapter in the ERTS User's Guide.

                logical_processors:
                  Returns the detected number of logical processors configured on the system. The
                  return  value  is either an integer, or the atom unknown if the emulator wasn't
                  able to detect logical processors configured.

                logical_processors_available:
                  Returns the detected number of  logical  processors  available  to  the  Erlang
                  runtime  system.  The return value is either an integer, or the atom unknown if
                  the emulator wasn't able to detect logical processors available. The number  of
                  logical  processors  available  is  less than or equal to the number of logical
                  processors online.

                logical_processors_online:
                  Returns the detected number of logical processors online  on  the  system.  The
                  return  value  is either an integer, or the atom unknown if the emulator wasn't
                  able to detect logical processors online.  The  number  of  logical  processors
                  online is less than or equal to the number of logical processors configured.

                machine:
                  Returns a string containing the Erlang machine name.

                min_heap_size:
                  Returns  {min_heap_size,  MinHeapSize}  where MinHeapSize is the current system
                  wide minimum heap size for spawned processes.

                min_bin_vheap_size:
                  Returns {min_bin_vheap_size,  MinBinVHeapSize}  where  MinBinVHeapSize  is  the
                  current system wide minimum binary virtual heap size for spawned processes.

                modified_timing_level:
                  Returns  the  modified  timing  level  (an integer) if modified timing has been
                  enabled;  otherwise,  undefined.  See  the  +T  command  line   flag   in   the
                  documentation of the erl(1) command for more information on modified timing.

                multi_scheduling:
                  Returns disabled, blocked, or enabled. A description of the return values:

                  disabled:
                    The  emulator  has  only one scheduler thread. The emulator does not have SMP
                    support, or have been started with only one scheduler thread.

                  blocked:
                    The emulator has more than one scheduler thread, but  all  scheduler  threads
                    but  one  have  been  blocked,  i.e., only one scheduler thread will schedule
                    Erlang processes and execute Erlang code.

                  enabled:
                    The emulator has more than one scheduler thread,  and  no  scheduler  threads
                    have been blocked, i.e., all available scheduler threads will schedule Erlang
                    processes and execute Erlang code.

                  See        also        erlang:system_flag(multi_scheduling,        BlockState),
                  erlang:system_info(multi_scheduling_blockers),                              and
                  erlang:system_info(schedulers).

                multi_scheduling_blockers:
                  Returns a list of PIDs when multi-scheduling is blocked; otherwise,  the  empty
                  list.  The  PIDs in the list is PIDs of the processes currently blocking multi-
                  scheduling. A PID  will  only  be  present  once  in  the  list,  even  if  the
                  corresponding process has blocked multiple times.

                  See        also        erlang:system_flag(multi_scheduling,        BlockState),
                  erlang:system_info(multi_scheduling), and erlang:system_info(schedulers).

                otp_release:
                  Returns a string containing the OTP release number.

                port_parallelism:
                  Returns the default port parallelism scheduling hint used. For more information
                  see the +spp command line argument of erl(1).

                port_count:
                  Returns the number of ports currently existing at the local node as an integer.
                  The same value as length(erlang:ports()) returns, but more efficient.

                port_limit:
                  Returns the maximum number of simultaneously existing ports at the  local  node
                  as  an integer. This limit can be configured at startup by using the +Q command
                  line flag of erl(1).

                process_count:
                  Returns the number of processes currently existing at  the  local  node  as  an
                  integer. The same value as length(processes()) returns, but more efficient.

                process_limit:
                  Returns  the  maximum  number of simultaneously existing processes at the local
                  node as an integer. This limit can be configured at startup  by  using  the  +P
                  command line flag of erl(1).

                procs:
                  Returns  a binary containing a string of process and port information formatted
                  as in Erlang crash dumps. For more information see the "How  to  interpret  the
                  Erlang crash dumps" chapter in the ERTS User's Guide.

                scheduler_bind_type:
                  Returns  information  on  how  user has requested schedulers to be bound or not
                  bound.

                  NOTE: Even though user has requested schedulers to be bound,  they  might  have
                  silently  failed  to  bind.  In order to inspect actual scheduler bindings call
                  erlang:system_info(scheduler_bindings).

                  For  more  information,  see  the  erl  +sbt   command   line   argument,   and
                  erlang:system_info(scheduler_bindings).

                scheduler_bindings:
                  Returns information on currently used scheduler bindings.

                  A  tuple  of  a  size  equal to erlang:system_info(schedulers) is returned. The
                  elements of the tuple are integers  or  the  atom  unbound.  Logical  processor
                  identifiers  are  represented  as integers. The Nth element of the tuple equals
                  the current binding for the scheduler with the scheduler identifier equal to N.
                  E.g.,        if        the        schedulers       have       been       bound,
                  element(erlang:system_info(scheduler_id),
                  erlang:system_info(scheduler_bindings))  will  return  the  identifier  of  the
                  logical processor that the calling process is executing on.

                  Note that only schedulers online can be bound to logical processors.

                  For   more   information,   see   the   erl   +sbt   command   line   argument,
                  erlang:system_info(schedulers_online).

                scheduler_id:
                  Returns the scheduler id (SchedulerId) of the scheduler thread that the calling
                  process is executing  on.  SchedulerId  is  a  positive  integer;  where  1  <=
                  SchedulerId       <=       erlang:system_info(schedulers).       See       also
                  erlang:system_info(schedulers).

                schedulers:
                  Returns the number of scheduler threads used by the emulator. Scheduler threads
                  online schedules Erlang processes and Erlang ports, and execute Erlang code and
                  Erlang linked in driver code.

                  The number of scheduler threads is determined at emulator boot time and  cannot
                  be  changed  after that. The amount of schedulers online can however be changed
                  at any time.

                  See     also      erlang:system_flag(schedulers_online,      SchedulersOnline),
                  erlang:system_info(schedulers_online),        erlang:system_info(scheduler_id),
                  erlang:system_flag(multi_scheduling,                               BlockState),
                  erlang:system_info(multi_scheduling),                  and                  and
                  erlang:system_info(multi_scheduling_blockers).

                schedulers_online:
                  Returns  the  amount  of  schedulers  online.  The  scheduler  identifiers   of
                  schedulers  online  satisfy  the  following  relationship:  1 <= SchedulerId <=
                  erlang:system_info(schedulers_online).

                  For    more    information,     see     erlang:system_info(schedulers),     and
                  erlang:system_flag(schedulers_online, SchedulersOnline).

                erlang:system_info(Item :: threads) -> boolean()

                smp_support:
                  Returns  true  if  the  emulator has been compiled with smp support; otherwise,
                  false.

                system_version:
                  Returns a string containing version number and some important  properties  such
                  as the number of schedulers.

                system_architecture:
                  Returns  a  string containing the processor and OS architecture the emulator is
                  built for.

                threads:
                  Returns true if the emulator has been compiled with thread support;  otherwise,
                  false is returned.

                thread_pool_size:
                  Returns  the  number  of  async  threads  in  the  async  thread  pool used for
                  asynchronous driver calls (driver_async()) as an integer.

                trace_control_word:
                  Returns the value of the node's trace control word. For  more  information  see
                  documentation of the function get_tcw in "Match Specifications in Erlang", ERTS
                  User's Guide.

                update_cpu_info:
                  The runtime system rereads  the  CPU  information  available  and  updates  its
                  internally stored information about the detected CPU topology and the amount of
                  logical processors configured, online, and available. If  the  CPU  information
                  has  changed  since  the  last  time it was read, the atom changed is returned;
                  otherwise, the atom unchanged is returned. If the CPU information  has  changed
                  you probably want to adjust the amount of schedulers online. You typically want
                  to have as many schedulers online as logical processors available.

                version:
                  Returns a string containing the version number of the emulator.

                wordsize:
                  Same as {wordsize, internal}.

                {wordsize, internal}:
                  Returns the size of Erlang term words in bytes as an integer, i.e. on a  32-bit
                  architecture 4 is returned, and on a pure 64-bit architecture 8 is returned. On
                  a halfword 64-bit emulator, 4 is returned, as the Erlang terms are stored using
                  a virtual wordsize of half the system's wordsize.

                {wordsize, external}:
                  Returns the true wordsize of the emulator, i.e. the size of a pointer, in bytes
                  as an integer. On a pure 32-bit architecture 4 is returned, on both a  halfword
                  and pure 64-bit architecture, 8 is returned.

          Note:
              The  scheduler  argument  has  changed name to scheduler_id. This in order to avoid
              mixup with the schedulers argument. The scheduler argument was introduced  in  ERTS
              version 5.5 and renamed in ERTS version 5.5.1.

       erlang:system_monitor() -> MonSettings

              Types:

                 MonSettings = undefined | {MonitorPid, Options}
                 MonitorPid = pid()
                 Options = [system_monitor_option()]
                 system_monitor_option() = busy_port
                                         | busy_dist_port
                                         | {long_gc, integer() >= 0}
                                         | {long_schedule, integer() >= 0}
                                         | {large_heap, integer() >= 0}

              Returns  the  current  system monitoring settings set by erlang:system_monitor/2 as
              {MonitorPid, Options}, or undefined if there are no  settings.  The  order  of  the
              options may be different from the one that was set.

       erlang:system_monitor(Arg) -> MonSettings

              Types:

                 Arg = MonSettings = undefined | {MonitorPid, Options}
                 MonitorPid = pid()
                 Options = [system_monitor_option()]
                 system_monitor_option() = busy_port
                                         | busy_dist_port
                                         | {long_gc, integer() >= 0}
                                         | {long_schedule, integer() >= 0}
                                         | {large_heap, integer() >= 0}

              When called with the argument undefined, all system performance monitoring settings
              are cleared.

              Calling the function with {MonitorPid, Options} as argument, is the same as calling
              erlang:system_monitor(MonitorPid, Options).

              Returns the previous system monitor settings just like erlang:system_monitor/0.

       erlang:system_monitor(MonitorPid, Options) -> MonSettings

              Types:

                 MonitorPid = pid()
                 Options = [system_monitor_option()]
                 MonSettings = undefined | {OldMonitorPid, OldOptions}
                 OldMonitorPid = pid()
                 OldOptions = [system_monitor_option()]
                 system_monitor_option() = busy_port
                                         | busy_dist_port
                                         | {long_gc, integer() >= 0}
                                         | {long_schedule, integer() >= 0}
                                         | {large_heap, integer() >= 0}

              Sets  system  performance  monitoring  options. MonitorPid is a local pid that will
              receive system monitor messages, and the second argument is a  list  of  monitoring
              options:

                {long_gc, Time}:
                  If   a  garbage  collection  in  the  system  takes  at  least  Time  wallclock
                  milliseconds, a message {monitor, GcPid, long_gc, Info} is sent to  MonitorPid.
                  GcPid  is  the pid that was garbage collected and Info is a list of two-element
                  tuples describing the result of the garbage collection. One of  the  tuples  is
                  {timeout, GcTime} where GcTime is the actual time for the garbage collection in
                  milliseconds. The other tuples  are  tagged  with  heap_size,  heap_block_size,
                  stack_size, mbuf_size, old_heap_size, and old_heap_block_size. These tuples are
                  explained  in  the  documentation  of   the   gc_start   trace   message   (see
                  erlang:trace/3).  New  tuples  may be added, and the order of the tuples in the
                  Info list may be changed at any time without prior notice.

                {long_schedule, Time}:
                  If a process or port in the system runs uninterrupted for at  least  Time  wall
                  clock milliseconds, a message {monitor, PidOrPort, long_schedule, Info} is sent
                  to MonitorPid. PidOrPort is the process or port that was running and Info is  a
                  list of two-element tuples describing the event. In case of a pid(), the tuples
                  {timeout, Millis}, {in, Location} and {out, Location} will  be  present,  where
                  Location  is  either an MFA ({Module, Function, Arity}) describing the function
                  where the process was scheduled in/out, or the atom undefined.  In  case  of  a
                  port(),  the tuples {timeout, Millis} and {port_op,Op} will be present. Op will
                  be one of proc_sig, timeout, input, output, event  or  dist_cmd,  depending  on
                  which  driver  callback  was  executing.  proc_sig is an internal operation and
                  should never appear,  while  the  others  represent  the  corresponding  driver
                  callbacks  timeout,  ready_input, ready_output, event and finally outputv (when
                  the port is used by distribution). The Millis value in the timeout  tuple  will
                  tell  you the actual uninterrupted execution time of the process or port, which
                  will always be >= the Time value supplied when starting the trace.  New  tuples
                  may be added to the Info list in the future, and the order of the tuples in the
                  list may be changed at any time without prior notice.

                  This can be used to detect problems with NIF's or drivers that take too long to
                  execute.  Generally,  1  ms  is  considered  a  good  maximum time for a driver
                  callback or a NIF. However, a  time  sharing  system  should  usually  consider
                  everything below 100 ms as "possible" and fairly "normal". Schedule times above
                  that might however indicate swapping  or  a  NIF/driver  that  is  misbehaving.
                  Misbehaving  NIF's  and  drivers  could  cause bad resource utilization and bad
                  overall performance of the system.

                {large_heap, Size}:
                  If a garbage collection in the system results in the allocated size of  a  heap
                  being at least Size words, a message {monitor, GcPid, large_heap, Info} is sent
                  to MonitorPid. GcPid and Info are the same as for long_gc  above,  except  that
                  the  tuple tagged with timeout is not present. Note: As of erts version 5.6 the
                  monitor message is sent if the sum of the sizes of all memory blocks  allocated
                  for  all  heap  generations  is  equal  to  or larger than Size. Previously the
                  monitor message was sent  if  the  memory  block  allocated  for  the  youngest
                  generation was equal to or larger than Size.

                busy_port:
                  If  a  process  in the system gets suspended because it sends to a busy port, a
                  message {monitor, SusPid, busy_port, Port} is sent to MonitorPid. SusPid is the
                  pid that got suspended when sending to Port.

                busy_dist_port:
                  If  a  process  in the system gets suspended because it sends to a process on a
                  remote node whose inter-node communication  was  handled  by  a  busy  port,  a
                  message  {monitor,  SusPid, busy_dist_port, Port} is sent to MonitorPid. SusPid
                  is the pid that got suspended when sending through the inter-node communication
                  port Port.

              Returns the previous system monitor settings just like erlang:system_monitor/0.

          Note:
              If a monitoring process gets so large that it itself starts to cause system monitor
              messages when garbage collecting, the messages will enlarge the  process's  message
              queue and probably make the problem worse.

              Keep  the  monitoring  process  neat  and  do not set the system monitor limits too
              tight.

              Failure: badarg if MonitorPid does not exist or is not a local process.

       erlang:system_profile() -> ProfilerSettings

              Types:

                 ProfilerSettings = undefined | {ProfilerPid, Options}
                 ProfilerPid = pid() | port()
                 Options = [system_profile_option()]
                 system_profile_option() = exclusive
                                         | runnable_ports
                                         | runnable_procs
                                         | scheduler

              Returns the current system profiling settings  set  by  erlang:system_profile/2  as
              {ProfilerPid,  Options},  or  undefined  if there are no settings. The order of the
              options may be different from the one that was set.

       erlang:system_profile(ProfilerPid, Options) -> ProfilerSettings

              Types:

                 ProfilerPid = pid() | port() | undefined
                 Options = [system_profile_option()]
                 ProfilerSettings = undefined
                                  | {pid() | port(), [system_profile_option()]}
                 system_profile_option() = exclusive
                                         | runnable_ports
                                         | runnable_procs
                                         | scheduler

              Sets system profiler options. ProfilerPid is a local pid or port that will  receive
              profiling  messages.  The  receiver  is  excluded  from  all  profiling. The second
              argument is a list of profiling options:

                exclusive:
                  If a synchronous call to a port from a process is done, the calling process  is
                  considered  not  runnable  during  the  call  runtime  to the port. The calling
                  process is notified as inactive and subsequently active when the port  callback
                  returns.

                runnable_procs:
                  If  a  process  is  put into or removed from the run queue a message, {profile,
                  Pid, State, Mfa, Ts},  is  sent  to  ProfilerPid.  Running  processes  that  is
                  reinserted into the run queue after having been preemptively scheduled out will
                  not trigger this message.

                runnable_ports:
                  If a port is put into or removed from the run queue a message, {profile,  Port,
                  State, 0, Ts}, is sent to ProfilerPid.

                scheduler:
                  If  a  scheduler  is put to sleep or awoken a message, {profile, scheduler, Id,
                  State, NoScheds, Ts}, is sent to ProfilerPid.

          Note:
              erlang:system_profile is considered experimental and its behaviour  may  change  in
              the future.

       term_to_binary(Term) -> ext_binary()

              Types:

                 Term = term()

              Returns  a binary data object which is the result of encoding Term according to the
              Erlang external term format.

              This can be used for a variety of purposes, for example writing a term to a file in
              an  efficient way, or sending an Erlang term to some type of communications channel
              not supported by distributed Erlang.

              See also binary_to_term/1.

       term_to_binary(Term, Options) -> ext_binary()

              Types:

                 Term = term()
                 Options =
                     [compressed |
                      {compressed, Level :: 0..9} |
                      {minor_version, Version :: 0..1}]

              Returns a binary data object which is the result of encoding Term according to  the
              Erlang external term format.

              If  the option compressed is provided, the external term format will be compressed.
              The compressed format is automatically recognized by binary_to_term/1  in  R7B  and
              later.

              It  is  also  possible  to  specify  a  compression  level  by  giving  the  option
              {compressed, Level}, where Level is an integer from 0 through 9. 0  means  that  no
              compression  will  be  done (it is the same as not giving any compressed option); 1
              will take the least time but may not compress as well as the higher levels; 9  will
              take  the  most  time  and  may  produce  a  smaller result. Note the "mays" in the
              preceding sentence; depending on the input term, level 9 compression may or may not
              produce a smaller result than level 1 compression.

              Currently, compressed gives the same result as {compressed, 6}.

              The  option  {minor_version,  Version}  can  be  use to control some details of the
              encoding. This option was introduced in R11B-4. Currently, the allowed  values  for
              Version are 0 and 1.

              {minor_version,  1}  forces  any  floats in the term to be encoded in a more space-
              efficient and exact way (namely in the 64-bit IEEE format, rather than converted to
              a  textual representation). binary_to_term/1 in R11B-4 and later is able decode the
              new representation.

              {minor_version, 0} is currently the default, meaning that floats  will  be  encoded
              using  a  textual  representation; this option is useful if you want to ensure that
              releases prior to R11B-4 can decode resulting binary.

              See also binary_to_term/1.

       throw(Any) -> no_return()

              Types:

                 Any = term()

              A non-local return from a function. If evaluated within a catch, catch will  return
              the value Any.

              > catch throw({hello, there}).
              {hello,there}

              Failure: nocatch if not evaluated within a catch.

       time() -> Time

              Types:

                 Time = calendar:time()

              Returns the current time as {Hour, Minute, Second}.

              The time zone and daylight saving time correction depend on the underlying OS.

              > time().
              {9,42,44}

       tl(List) -> term()

              Types:

                 List = [term(), ...]

              Returns the tail of List, that is, the list minus the first element.

              > tl([geesties, guilies, beasties]).
              [guilies, beasties]

              Allowed in guard tests.

              Failure: badarg if List is the empty list [].

       erlang:trace(PidSpec, How, FlagList) -> integer()

              Types:

                 PidSpec = pid() | existing | new | all
                 How = boolean()
                 FlagList = [trace_flag()]
                 trace_flag() = all
                              | send
                              | 'receive'
                              | procs
                              | call
                              | silent
                              | return_to
                              | running
                              | exiting
                              | garbage_collection
                              | timestamp
                              | cpu_timestamp
                              | arity
                              | set_on_spawn
                              | set_on_first_spawn
                              | set_on_link
                              | set_on_first_link
                              | {tracer, pid() | port()}

              Turns  on (if How == true) or off (if How == false) the trace flags in FlagList for
              the process or processes represented by PidSpec.

              PidSpec is either a pid for a local process, or one of the following atoms:

                existing:
                  All processes currently existing.

                new:
                  All processes that will be created in the future.

                all:
                  All currently existing processes and all processes that will be created in  the
                  future.

              FlagList  can  contain any number of the following flags (the "message tags" refers
              to the list of messages following below):

                all:
                  Set all trace flags except {tracer, Tracer} and cpu_timestamp that are in their
                  nature different than the others.

                send:
                  Trace sending of messages.

                  Message tags: send, send_to_non_existing_process.

                'receive':
                  Trace receiving of messages.

                  Message tags: 'receive'.

                procs:
                  Trace process related events.

                  Message  tags: spawn, exit, register, unregister, link, unlink, getting_linked,
                  getting_unlinked.

                call:
                  Trace certain function calls. Specify which function calls to trace by  calling
                  erlang:trace_pattern/3.

                  Message tags: call, return_from.

                silent:
                  Used  in  conjunction  with  the  call  trace  flag.  The call, return_from and
                  return_to trace messages are inhibited if this flag is set, but  if  there  are
                  match specs they are executed as normal.

                  Silent mode is inhibited by executing erlang:trace(_, false, [silent|_]), or by
                  a match spec executing the {silent, false} function.

                  The silent trace flag facilitates setting up  a  trace  on  many  or  even  all
                  processes  in  the  system.  Then  the  interesting  trace can be activated and
                  deactivated using the {silent,Bool} match spec function, giving a  high  degree
                  of control of which functions with which arguments that triggers the trace.

                  Message tags: call, return_from, return_to. Or rather, the absence of.

                return_to:
                  Used  in  conjunction  with the call trace flag. Trace the actual return from a
                  traced function back to its caller. Only works for functions  traced  with  the
                  local option to erlang:trace_pattern/3.

                  The  semantics  is  that  a  trace  message is sent when a call traced function
                  actually returns, that is, when a chain of tail recursive calls is ended. There
                  will  be only one trace message sent per chain of tail recursive calls, why the
                  properties of tail recursiveness for function calls are kept while tracing with
                  this  flag.  Using  call and return_to trace together makes it possible to know
                  exactly in which function a process executes at any time.

                  To get  trace  messages  containing  return  values  from  functions,  use  the
                  {return_trace} match_spec action instead.

                  Message tags: return_to.

                running:
                  Trace scheduling of processes.

                  Message tags: in, and out.

                exiting:
                  Trace scheduling of an exiting processes.

                  Message tags: in_exiting, out_exiting, and out_exited.

                garbage_collection:
                  Trace garbage collections of processes.

                  Message tags: gc_start, gc_end.

                timestamp:
                  Include  a time stamp in all trace messages. The time stamp (Ts) is of the same
                  form as returned by erlang:now().

                cpu_timestamp:
                  A global trace flag for the Erlang node that makes all trace timestamps  be  in
                  CPU  time,  not  wallclock.  It  is only allowed with PidSpec==all. If the host
                  machine  operating  system  does  not  support   high   resolution   CPU   time
                  measurements, trace/3 exits with badarg.

                arity:
                  Used  in  conjunction with the call trace flag. {M, F, Arity} will be specified
                  instead of {M, F, Args} in call trace messages.

                set_on_spawn:
                  Makes any process  created  by  a  traced  process  inherit  its  trace  flags,
                  including the set_on_spawn flag.

                set_on_first_spawn:
                  Makes  the  first  process created by a traced process inherit its trace flags,
                  excluding the set_on_first_spawn flag.

                set_on_link:
                  Makes any process linked by a traced process inherit its trace flags, including
                  the set_on_link flag.

                set_on_first_link:
                  Makes  the first process linked to by a traced process inherit its trace flags,
                  excluding the set_on_first_link flag.

                {tracer, Tracer}:
                  Specify where to send the trace messages. Tracer must be the  pid  of  a  local
                  process  or  the  port  identifier  of a local port. If this flag is not given,
                  trace messages will be sent to the process that called erlang:trace/3.

              The effect of combining set_on_first_link with set_on_link is the  same  as  having
              set_on_first_link alone. Likewise for set_on_spawn and set_on_first_spawn.

              If  the  timestamp  flag  is  not given, the tracing process will receive the trace
              messages described below. Pid is the pid of the traced process in which the  traced
              event has occurred. The third element of the tuple is the message tag.

              If  the  timestamp  flag  is given, the first element of the tuple will be trace_ts
              instead and the timestamp is added last in the tuple.

                {trace, Pid, 'receive', Msg}:
                  When Pid receives the message Msg.

                {trace, Pid, send, Msg, To}:
                  When Pid sends the message Msg to the process To.

                {trace, Pid, send_to_non_existing_process, Msg, To}:
                  When Pid sends the message Msg to the non-existing process To.

                {trace, Pid, call, {M, F, Args}}:
                  When Pid calls a  traced  function.  The  return  values  of  calls  are  never
                  supplied, only the call and its arguments.

                  Note  that  the  trace  flag  arity  can be used to change the contents of this
                  message, so that Arity is specified instead of Args.

                {trace, Pid, return_to, {M, F, Arity}}:
                  When Pid returns to the specified function. This trace message is sent if  both
                  the  call and the return_to flags are set, and the function is set to be traced
                  on local function calls. The message is only sent when returning from  a  chain
                  of tail recursive function calls where at least one call generated a call trace
                  message (that is, the  functions  match  specification  matched  and  {message,
                  false} was not an action).

                {trace, Pid, return_from, {M, F, Arity}, ReturnValue}:
                  When Pid returns from the specified function. This trace message is sent if the
                  call  flag  is  set,  and  the  function  has  a  match  specification  with  a
                  return_trace or exception_trace action.

                {trace, Pid, exception_from, {M, F, Arity}, {Class, Value}}:
                  When  Pid  exits  from  the  specified function due to an exception. This trace
                  message is sent if the  call  flag  is  set,  and  the  function  has  a  match
                  specification with an exception_trace action.

                {trace, Pid, spawn, Pid2, {M, F, Args}}:
                  When  Pid  spawns  a new process Pid2 with the specified function call as entry
                  point.

                  Note that Args is supposed to be the argument list, but may be any term in  the
                  case of an erroneous spawn.

                {trace, Pid, exit, Reason}:
                  When Pid exits with reason Reason.

                {trace, Pid, link, Pid2}:
                  When Pid links to a process Pid2.

                {trace, Pid, unlink, Pid2}:
                  When Pid removes the link from a process Pid2.

                {trace, Pid, getting_linked, Pid2}:
                  When Pid gets linked to a process Pid2.

                {trace, Pid, getting_unlinked, Pid2}:
                  When Pid gets unlinked from a process Pid2.

                {trace, Pid, register, RegName}:
                  When Pid gets the name RegName registered.

                {trace, Pid, unregister, RegName}:
                  When   Pid  gets  the  name  RegName  unregistered.  Note  that  this  is  done
                  automatically when a registered process exits.

                {trace, Pid, in, {M, F, Arity} | 0}:
                  When Pid is scheduled to run. The process will run in function {M,  F,  Arity}.
                  On some rare occasions the current function cannot be determined, then the last
                  element Arity is 0.

                {trace, Pid, out, {M, F, Arity} | 0}:
                  When Pid is scheduled out. The process was running in function {M,  F,  Arity}.
                  On some rare occasions the current function cannot be determined, then the last
                  element Arity is 0.

                {trace, Pid, gc_start, Info}:
                  Sent when garbage collection is about to be started. Info is  a  list  of  two-
                  element  tuples, where the first element is a key, and the second is the value.
                  You should not depend on the tuples have  any  defined  order.  Currently,  the
                  following keys are defined:

                  heap_size:
                    The size of the used part of the heap.

                  heap_block_size:
                    The size of the memory block used for storing the heap and the stack.

                  old_heap_size:
                    The size of the used part of the old heap.

                  old_heap_block_size:
                    The size of the memory block used for storing the old heap.

                  stack_size:
                    The actual size of the stack.

                  recent_size:
                    The size of the data that survived the previous garbage collection.

                  mbuf_size:
                    The combined size of message buffers associated with the process.

                  bin_vheap_size:
                    The total size of unique off-heap binaries referenced from the process heap.

                  bin_vheap_block_size:
                    The  total  size  of  binaries,  in words, allowed in the virtual heap in the
                    process before doing a garbage collection.

                  bin_old_vheap_size:
                    The total size of unique off-heap binaries referenced from  the  process  old
                    heap.

                  bin_vheap_block_size:
                    The  total size of binaries, in words, allowed in the virtual old heap in the
                    process before doing a garbage collection.

                  All sizes are in words.

                {trace, Pid, gc_end, Info}:
                  Sent when garbage collection is finished. Info contains the same kind  of  list
                  as  in  the gc_start message, but the sizes reflect the new sizes after garbage
                  collection.

              If the tracing process dies, the flags will be silently removed.

              Only one process can trace a particular process. For this reason, attempts to trace
              an already traced process will fail.

              Returns:  A  number  indicating  the  number  of processes that matched PidSpec. If
              PidSpec is a pid, the return value will be 1. If PidSpec is  all  or  existing  the
              return  value  will be the number of processes running, excluding tracer processes.
              If PidSpec is new, the return value will be 0.

              Failure: If specified arguments are not supported. For example cpu_timestamp is not
              supported on all platforms.

       erlang:trace_delivered(Tracee) -> Ref

              Types:

                 Tracee = pid() | all
                 Ref = reference()

              The  delivery  of  trace  messages is dislocated on the time-line compared to other
              events in the system. If you know that the Tracee has passed some specific point in
              its  execution, and you want to know when at least all trace messages corresponding
              to  events  up  to   this   point   have   reached   the   tracer   you   can   use
              erlang:trace_delivered(Tracee). A {trace_delivered, Tracee, Ref} message is sent to
              the caller of erlang:trace_delivered(Tracee) when it is guaranteed that  all  trace
              messages  have  been  delivered  to  the tracer up to the point that the Tracee had
              reached at the time of the call to erlang:trace_delivered(Tracee).

              Note that the trace_delivered message does not imply that trace messages have  been
              delivered;  instead,  it  implies  that all trace messages that should be delivered
              have been delivered. It is not an error if Tracee isn't, and hasn't been traced  by
              someone,  but  if this is the case, no trace messages will have been delivered when
              the trace_delivered message arrives.

              Note that Tracee has to refer to a process currently, or previously existing on the
              same  node  as the caller of erlang:trace_delivered(Tracee) resides on. The special
              Tracee atom all denotes all processes that currently are traced in the node.

              An example: Process A is Tracee, port B is tracer, and process C is the port  owner
              of  B. C wants to close B when A exits. C can ensure that the trace isn't truncated
              by  calling   erlang:trace_delivered(A)   when   A   exits   and   wait   for   the
              {trace_delivered, A, Ref} message before closing B.

              Failure:  badarg  if Tracee does not refer to a process (dead or alive) on the same
              node as the caller of erlang:trace_delivered(Tracee) resides on.

       erlang:trace_info(PidOrFunc, Item) -> Res

              Types:

                 PidOrFunc = pid() | new | {Module, Function, Arity} | on_load
                 Module = module()
                 Function = atom()
                 Arity = arity()
                 Item = flags
                      | tracer
                      | traced
                      | match_spec
                      | meta
                      | meta_match_spec
                      | call_count
                      | call_time
                      | all
                 Res = trace_info_return()
                 trace_info_return() = undefined
                                     | {flags, [trace_info_flag()]}
                                     | {tracer, pid() | port() | []}
                                     | trace_info_item_result()
                                     | {all,
                                        [trace_info_item_result()] |
                                        false |
                                        undefined}
                 trace_info_item_result() = {traced,
                                             global | local | false | undefined}
                                          | {match_spec,
                                             trace_match_spec() |
                                             false |
                                             undefined}
                                          | {meta,
                                             pid() |
                                             port() |
                                             false |
                                             undefined |
                                             []}
                                          | {meta_match_spec,
                                             trace_match_spec() |
                                             false |
                                             undefined}
                                          | {call_count,
                                             integer() >= 0 |
                                             boolean() |
                                             undefined}
                                          | {call_time,
                                             [{pid(),
                                               integer() >= 0,
                                               integer() >= 0,
                                               integer() >= 0}] |
                                             boolean() |
                                             undefined}
                 trace_info_flag() = send
                                   | 'receive'
                                   | set_on_spawn
                                   | call
                                   | return_to
                                   | procs
                                   | set_on_first_spawn
                                   | set_on_link
                                   | running
                                   | garbage_collection
                                   | timestamp
                                   | arity
                 trace_match_spec() = [{[term()] | '_', [term()], [term()]}]

              Returns trace information about a process or function.

              To get information about a process, PidOrFunc should be a pid or the atom new.  The
              atom  new  means  that  the default trace state for processes to be created will be
              returned. Item must have one of the following values:

                flags:
                  Return a list of atoms indicating what  kind  of  traces  is  enabled  for  the
                  process.  The  list  will be empty if no traces are enabled, and one or more of
                  the followings atoms if traces  are  enabled:  send,  'receive',  set_on_spawn,
                  call,    return_to,    procs,    set_on_first_spawn,    set_on_link,   running,
                  garbage_collection, timestamp, and arity. The order is arbitrary.

                tracer:
                  Return the identifier for process or port tracing this process. If this process
                  is not being traced, the return value will be [].

              To  get  information  about  a function, PidOrFunc should be a three-element tuple:
              {Module, Function, Arity} or the atom on_load. No wildcards  are  allowed.  Returns
              undefined  if the function does not exist or false if the function is not traced at
              all. Item must have one of the following values:

                traced:
                  Return global if this function is traced on global  function  calls,  local  if
                  this  function is traced on local function calls (i.e local and global function
                  calls), and false if neither local nor global function calls are traced.

                match_spec:
                  Return the match specification for  this  function,  if  it  has  one.  If  the
                  function  is locally or globally traced but has no match specification defined,
                  the returned value is [].

                meta:
                  Return the meta trace tracer process or port for this function, if it has  one.
                  If  the  function  is  not  meta traced the returned value is false, and if the
                  function is meta traced but has once detected that the tracer proc is  invalid,
                  the returned value is [].

                meta_match_spec:
                  Return  the meta trace match specification for this function, if it has one. If
                  the function is meta  traced  but  has  no  match  specification  defined,  the
                  returned value is [].

                call_count:
                  Return  the  call count value for this function or true for the pseudo function
                  on_load if call count tracing is  active.  Return  false  otherwise.  See  also
                  erlang:trace_pattern/3.

                call_time:
                  Return  the  call time values for this function or true for the pseudo function
                  on_load if call time tracing is active. Returns false otherwise. The call  time
                  values  returned,  [{Pid,  Count,  S,  Us}], is a list of each process that has
                  executed   the   function    and    its    specific    counters.    See    also
                  erlang:trace_pattern/3.

                all:
                  Return  a  list  containing  the  {Item,  Value} tuples for all other items, or
                  return false if no tracing is active for this function.

              The actual return value will  be  {Item,  Value},  where  Value  is  the  requested
              information  as described above. If a pid for a dead process was given, or the name
              of a non-existing function, Value will be undefined.

              If PidOrFunc is the on_load, the information returned refers to the  default  value
              for code that will be loaded.

       erlang:trace_pattern(MFA, MatchSpec) -> integer() >= 0

              Types:

                 MFA = trace_pattern_mfa()
                 MatchSpec = (MatchSpecList :: trace_match_spec())
                           | boolean()
                           | restart
                           | pause
                 trace_pattern_mfa() = {atom(), atom(), arity() | '_'} | on_load
                 trace_match_spec() = [{[term()] | '_', [term()], [term()]}]

              The  same  as  erlang:trace_pattern(MFA,  MatchSpec,  []),  retained  for  backward
              compatibility.

       erlang:trace_pattern(MFA, MatchSpec, FlagList) ->
                               integer() >= 0

              Types:

                 MFA = trace_pattern_mfa()
                 MatchSpec = (MatchSpecList :: trace_match_spec())
                           | boolean()
                           | restart
                           | pause
                 FlagList = [trace_pattern_flag()]
                 trace_pattern_mfa() = {atom(), atom(), arity() | '_'} | on_load
                 trace_match_spec() = [{[term()] | '_', [term()], [term()]}]
                 trace_pattern_flag() = global
                                      | local
                                      | meta
                                      | {meta, Pid :: pid()}
                                      | call_count
                                      | call_time

              This BIF is used to enable or disable call tracing for exported functions. It  must
              be  combined  with  erlang:trace/3  to  set  the  call  trace  flag for one or more
              processes.

              Conceptually, call tracing works like this: Inside the Erlang virtual machine there
              is  a  set  of  processes to be traced and a set of functions to be traced. Tracing
              will be enabled on the intersection of the set. That is, if a process  included  in
              the  traced  process  set calls a function included in the traced function set, the
              trace action will be taken. Otherwise, nothing will happen.

              Use erlang:trace/3 to add or remove one or more processes  to  the  set  of  traced
              processes.  Use  erlang:trace_pattern/2  to add or remove exported functions to the
              set of traced functions.

              The erlang:trace_pattern/3 BIF can also add match  specifications  to  an  exported
              function.  A  match  specification  comprises  a  pattern that the arguments to the
              function must match, a guard expression which must evaluate to true and  an  action
              to be performed. The default action is to send a trace message. If the pattern does
              not match or the guard fails, the action will not be executed.

              The MFA argument should be a tuple like  {Module,  Function,  Arity}  or  the  atom
              on_load  (described  below).  It  can  be  the  module,  function, and arity for an
              exported function (or a BIF in any module). The '_' atom can be used to mean any of
              that kind. Wildcards can be used in any of the following ways:

                {Module,Function,'_'}:
                  All exported functions of any arity named Function in module Module.

                {Module,'_','_'}:
                  All exported functions in module Module.

                {'_','_','_'}:
                  All exported functions in all loaded modules.

              Other  combinations,  such  as {Module,'_',Arity}, are not allowed. Local functions
              will match wildcards only if the local option is in the FlagList.

              If the MFA argument is the atom on_load, the match specification and flag list will
              be used on all modules that are newly loaded.

              The MatchSpec argument can take any of the following forms:

                false:
                  Disable  tracing  for the matching function(s). Any match specification will be
                  removed.

                true:
                  Enable tracing for the matching function(s).

                MatchSpecList:
                  A list of match specifications. An empty list is equivalent to  true.  See  the
                  ERTS User's Guide for a description of match specifications.

                restart:
                  For  the  FlagList  option  call_count  and  call_time:  restart  the  existing
                  counters. The behaviour is undefined for other FlagList options.

                pause:
                  For the FlagList option call_count and call_time: pause the existing  counters.
                  The behaviour is undefined for other FlagList options.

              The FlagList parameter is a list of options. The following options are allowed:

                global:
                  Turn  on  or  off  call  tracing  for  global  function  calls  (that is, calls
                  specifying the module explicitly). Only exported functions will match and  only
                  global calls will generate trace messages. This is the default.

                local:
                  Turn  on  or  off  call tracing for all types of function calls. Trace messages
                  will be sent whenever any of the specified functions are called, regardless  of
                  how  they are called. If the return_to flag is set for the process, a return_to
                  message will also be sent when this function returns to its caller.

                meta | {meta, Pid}:
                  Turn on or off meta tracing for all types of  function  calls.  Trace  messages
                  will  be  sent  to the tracer process or port Pid whenever any of the specified
                  functions are called,  regardless  of  how  they  are  called.  If  no  Pid  is
                  specified, self() is used as a default tracer process.

                  Meta  tracing  traces  all  processes and does not care about the process trace
                  flags set by trace/3, the trace flags are instead fixed to [call, timestamp].

                  The match spec function {return_trace} works with meta trace and send its trace
                  message to the same tracer process.

                call_count:
                  Starts (MatchSpec == true) or stops (MatchSpec == false) call count tracing for
                  all types of function calls. For every function a counter is  incremented  when
                  the  function  is  called,  in  any  process. No process trace flags need to be
                  activated.

                  If call count tracing is started while already running, the count is  restarted
                  from  zero.  Running counters can be paused with MatchSpec == pause. Paused and
                  running counters can be restarted from zero with MatchSpec == restart.

                  The counter value can be read with erlang:trace_info/2.

                call_time:
                  Starts (MatchSpec == true) or stops (MatchSpec == false) call time tracing  for
                  all  types  of function calls. For every function a counter is incremented when
                  the function is called. Time spent in the function is accumulated in two  other
                  counters,  seconds  and  micro-seconds.  The  counters are stored for each call
                  traced process.

                  If call time tracing is started while already running, the count  and  time  is
                  restarted  from  zero.  Running counters can be paused with MatchSpec == pause.
                  Paused and running counters can  be  restarted  from  zero  with  MatchSpec  ==
                  restart.

                  The counter value can be read with erlang:trace_info/2.

              The  global  and local options are mutually exclusive and global is the default (if
              no options are specified). The call_count and meta options perform a kind of  local
              tracing,  and  can  also  not  be  combined  with  global. A function can be either
              globally or locally traced. If global tracing is specified for a specified  set  of
              functions;  local,  meta,  call time and call count tracing for the matching set of
              local functions will be disabled, and vice versa.

              When disabling trace, the option must match the type of trace that is  set  on  the
              function,  so  that local tracing must be disabled with the local option and global
              tracing with the global option (or no option at all), and so forth.

              There is no way to directly change  part  of  a  match  specification  list.  If  a
              function  has  a match specification, you can replace it with a completely new one.
              If you need to change an existing match specification, use the  erlang:trace_info/2
              BIF to retrieve the existing match specification.

              Returns  the  number of exported functions that matched the MFA argument. This will
              be zero if none matched at all.

       trunc(Number) -> integer()

              Types:

                 Number = number()

              Returns an integer by the truncating Number.

              > trunc(5.5).
              5

              Allowed in guard tests.

       tuple_size(Tuple) -> integer() >= 0

              Types:

                 Tuple = tuple()

              Returns an integer which is the number of elements in Tuple.

              > tuple_size({morni, mulle, bwange}).
              3

              Allowed in guard tests.

       tuple_to_list(Tuple) -> [term()]

              Types:

                 Tuple = tuple()

              Returns a list which corresponds to Tuple. Tuple may contain any Erlang terms.

              > tuple_to_list({share, {'Ericsson_B', 163}}).
              [share,{'Ericsson_B',163}]

       erlang:universaltime() -> DateTime

              Types:

                 DateTime = calendar:datetime()

              Returns the current date and time according to Universal  Time  Coordinated  (UTC),
              also  called  GMT,  in  the  form  {{Year,  Month, Day}, {Hour, Minute, Second}} if
              supported by the underlying operating system.  If  not,  erlang:universaltime()  is
              equivalent to erlang:localtime().

              > erlang:universaltime().
              {{1996,11,6},{14,18,43}}

       erlang:universaltime_to_localtime(Universaltime) -> Localtime

              Types:

                 Localtime = Universaltime = calendar:datetime()

              Converts  Universal Time Coordinated (UTC) date and time to local date and time, if
              this is supported by the underlying OS.  Otherwise,  no  conversion  is  done,  and
              Universaltime is returned.

              > erlang:universaltime_to_localtime({{1996,11,6},{14,18,43}}).
              {{1996,11,7},{15,18,43}}

              Failure: badarg if Universaltime does not denote a valid date and time.

       unlink(Id) -> true

              Types:

                 Id = pid() | port()

              Removes  the  link, if there is one, between the calling process and the process or
              port referred to by Id.

              Returns true and does not fail, even if there is no link to Id, or if Id  does  not
              exist.

              Once  unlink(Id) has returned it is guaranteed that the link between the caller and
              the entity referred to by Id has no effect on the caller in the future (unless  the
              link  is  setup again). If caller is trapping exits, an {'EXIT', Id, _} message due
              to the link might have been placed in the caller's message queue prior to the call,
              though.  Note,  the  {'EXIT', Id, _} message can be the result of the link, but can
              also be the result of Id calling  exit/2.  Therefore,  it  may  be  appropriate  to
              cleanup  the  message  queue  when  trapping exits after the call to unlink(Id), as
              follow:

                  unlink(Id),
                  receive
                      {'EXIT', Id, _} ->
                          true
                  after 0 ->
                          true
                  end

          Note:
              Prior  to  OTP  release  R11B  (erts  version  5.5)  unlink/1  behaved   completely
              asynchronous,  i.e.,  the  link  was  active  until the "unlink signal" reached the
              linked entity. This had one undesirable effect, though. You could never  know  when
              you were guaranteed not to be effected by the link.

              Current  behavior  can be viewed as two combined operations: asynchronously send an
              "unlink signal" to the linked entity and ignore any future results of the link.

       unregister(RegName) -> true

              Types:

                 RegName = atom()

              Removes the registered name RegName, associated with a pid or a port identifier.

              > unregister(db).
              true

              Users are advised not to unregister system processes.

              Failure: badarg if RegName is not a registered name.

       whereis(RegName) -> pid() | port() | undefined

              Types:

                 RegName = atom()

              Returns the pid or port  identifier  with  the  registered  name  RegName.  Returns
              undefined if the name is not registered.

              > whereis(db).
              <0.43.0>

       erlang:yield() -> true

              Voluntarily   let  other  processes  (if  any)  get  a  chance  to  execute.  Using
              erlang:yield() is similar to receive after 1 -> ok  end,  except  that  yield()  is
              faster.

          Warning:
              There  is  seldom or never any need to use this BIF, especially in the SMP-emulator
              as other processes will have a chance to run in another  scheduler  thread  anyway.
              Using  this  BIF  without  a  thorough  grasp  of how the scheduler works may cause
              performance degradation.