Section 7,4: NOF77_EXTERNAL

 If you specify the -nof77 compiler option, you get an
 interpretation of the EXTERNAL statement that facilitates
 compatibility with older versions of Fortran.  (The ANSI FORTRAN-77
 interpretation is incompatible with the previous standard and
 previous Digital 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.