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

  If defined during compilation, this logical name changes the
  default file specification used to locate include files and text
  libraries from '.FOR' and '.TLB' to 'FORT$INCLUDE:.FOR' and
  'FORT$INCLUDE:.TLB', respectively.  It can be a search list.