/sys$common/syshlp/helplib.hlb FORTRAN, /F77  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  /[NO]F77                        D=/F77

  Controls whether FORTRAN-77 interpretation rules are used for those
  statements that have a meaning that is incompatible with
  FORTRAN-66.

  This qualifier can also be specified with the OPTIONS statement.
  The default is /F77.  If you specify /NOF77, the compiler selects
  FORTRAN-66 interpretations in cases of incompatibility.

  For an explanation of the incompatibilities, see your user manual.