The ARGUMENT function specifies an argument in a variable-length
  parameter list that was created using the LIST attribute.

  Syntax:

     ARGUMENT( parameter-name, n )

  The 'parameter-name' argument specifies the name of a  parameter
  declared  with the LIST attribute.  The 'n' specifies a positive
  integer value that identifies the argument.  The first  argument
  in  a  list  is always 1.  An error occurs if the value supplied
  for 'n' is less than  1,  or  exceeds  the  ARGUMENT_LIST_LENGTH
  parameter (which indicates the total number of arguments).

  If the LIST parameter is a value parameter,  ARGUMENT  indicates
  the  corresponding  value  in  the  argument  list.  If the LIST
  parameter is a VAR parameter, ARGUMENT is  a  reference  to  the
  corresponding variable in the argument list.