An implementation of finding higher-order critical pairs, inspired by work of
Tobias Nipkow.  Here, we code the program on a per-signature basis, rather
than once and for all, which is currently impossible in Elf without an
explicit representation for signatures.  The subdirectories contain individual
theories.  Note that Knuth-Bendix completion is not directly programmable,
because of the need to generalize before installing new rewrite rules.

Author: Frank Pfenning

Reference: Tobias Nipkow, Higher-Order Critical Pairs.  In: Sixth Annual
Symposium on Logic in Computer Science, pages 342--350, 1991.

utlam/  --- untyped lambda calculus
pair/	--- surjective pairing
