A function (synonymous with intrinsic function) is a temporary data
  item that represents a value to be determined at the time the
  function is referenced during the execution of a statement.  The
  value can be alphanumeric, numeric, or integer.

  A function-identifier is a syntactically correct combination of
  character strings and separators that uniquely references the data
  item resulting from the evaluation of a function.   Functions are
  treated as elementary data items, but cannot be  receiving operands. A
  function-identifier that references an alphanumeric function can be
  specified wherever an identifier is permitted and where a reference to
  a function is not specifically prohibited by general-format rules. An
  integer or numeric function can be used anywhere an arithmetic
  expression can be used, subject to certain restrictions.

  The general format of a function-identifier is as follows:

  FUNCTION function-name [({argument}... )] [reference-modifier]

  A function-name is one of the names listed below. Most function-names
  are key words but not reserved words (the exceptions are LENGTH,
  RANDOM, and SUM, which are reserved words, as is FUNCTION), and  can
  be used in a program outside the context of a function.

  An argument is an identifier (including a function-identifier),  a
  literal an arithmetic expression, or a table that complies with the
  specific rules governing the number, class, and category of arguments
  for the function.   The arguments in an argument list may be separated
  by a comma; they are evaluated individually, from left to right.

  A reference-modifier can be specified only for alphanumeric functions.
  It specifies the beginning character position and optionally the
  length of the resulting data item.

  The functions are listed below.  For a complete description of the
  functions, including their formats, see the chapter on Intrinsic
  Functions in the COBOL Reference Manual.

  ACOS               LENGTH         ORD-MIN*
  ANNUITY            LOG            PRESENT-VALUE*
  ARGCOUNT           LOG10          RANDOM
  ASIN               LOWER-CASE     RANGE*
  ATAN               MAX*           REM
  CHAR               MEAN*          REVERSE
  COS                MEDIAN*        SIN
  CURRENT-DATE       MIDRANGE*      SQRT
  DATE-OF-INTEGER    MIN*           STANDARD-DEVIATION*
  DAY-OF-INTEGER     MOD            SUM*
  FACTORIAL          NUMVAL         TAN
  INTEGER            NUMVAL-C       UPPER-CASE
  INTEGER-OF-DATE    ORD            VARIANCE*
  INTEGER-OF-DAY     ORD-MAX*       WHEN-COMPILED
  INTEGER-PART

  *Functions which permit a variable number of arguments which may
  include occurring items subscripted by "ALL" for one or more of
  its dimensions.

  In addition, five new Y2K functions are documented in the release notes:

  YEAR-TO-YYYY
  DATE-TO-YYYYMMDD
  DAY-TO-YYYYDDD
  TEST-DATE-YYYYMMDD
  TEST-DAY-YYYYMMDD