Defines a function consisting of a single expression.  The function
  must be invoked from the program unit in which it is defined.
  Format:

     fun([p [,p]...])=e

     fun  Is the symbolic name for the function. You can
          establish its type explicitly or implicitly. The
          value of the expression is returned to the function
          name when the function is invoked.

     p    Is an unsubscripted variable name specifying a
          dummy argument.  The arguments must agree in order,
          number, and type with the actual arguments of the
          statement invoking the function.

     e    Is an arithmetic, logical, or character expression.
          If the expression contains a reference to another
          statement function, the referenced statement
          function must precede the statement function
          containing the reference.

  Declarator information does not apply to a dummy argument except
  for type.  For example, you cannot define a dummy argument as an
  array or as part of a common block.

  If you use the name of a dummy argument outside the function
  statement, the name defines another separate data entity.

                                 NOTE

          This  statement  is  obsolescent  in  Fortran   95.
          HP  Fortran  flags  obsolescent  features,  but
          fully supports them.