An implementation of the type system of Forsythe.  This closely
follows the reported cited below.  A few minor items have not been
implemented, the most important perhaps is rec (which probably
has changed for more recent versions of Forsythe).

Author: Frank Pfenning

Reference: John C. Reynolds: Preliminary Design of the Programming Language
Forsythe, Carnegie Mellon University Technical Report CMU-CS-88-159, June
1988.

The encoding of quantified Boolean expressions:

John C. Reynolds: Even Typing Normal Forms Can Be Hard, talk given at the
North American Jumelage 1991, AT&T Bell Laboratories, Murray Hill, New Jersey.
