I just received the 1990 DEC Direct Software Solutions catalog which
on page 9.6 (section.page, DEC has not started numbering fractional
pages) lists Quintus Prolog for VAX, MicroVAX, and VAXstations with
2MB memory and 15MB disk (to be dedicated to Prolog). Pricing is not
listed, which probably means it does not meet one of the originally
posted requirements, but is available from DECDirect (800-343-4040).
This catalog lists only U.S. Sales Offices, but I'm sure your local
DEC rep would be happy to point you in the right direction.
(BTW: The catalog listing says Quintus Prolog runs on either VMS 5.1+
or Ultrix-32 3.0+)
I hope this information might be of some help.