/sys$common/syshlp/helplib.hlb FORTRAN, Compatibility Features, NOF77_EXTERNAL  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  If you specify the /NOF77 qualifier, you get an interpretation of
  the EXTERNAL statement that aids compatibility with older versions
  of Fortran.  (The ANSI FORTRAN-77 interpretation is incompatible
  with the previous standard and previous Compaq implementations.)

  The NOF77 interpretation combines the functionality of the
  INTRINSIC statement with that of the EXTERNAL statement discussed
  under the Help topic:  Statements EXTERNAL.

  The NOF77 EXTERNAL statement lets you use subprograms as arguments
  to other subprograms.  The subprograms to be used as arguments can
  be either user-supplied procedures or Fortran library functions.
  Statement format:

     EXTERNAL [*]v [,[*]v]...

     v  Is the symbolic name of a subprogram or the name of
        a dummy argument associated with the symbolic name
        of a subprogram.

     *  Specifies that a user-supplied function is to be used
        instead of a Fortran library function having the same
        name.

  The NOF77 EXTERNAL statement declares that each symbolic name in
  its list is an external procedure name.  Such a name can then be
  used as an actual argument to a subprogram, which in turn can use
  the corresponding dummy argument in a function reference or CALL
  statement.

  However, used as an argument, a complete function reference
  represents a value, not a subprogram name.