YAP is a high-performance Prolog compiler developed at LIACC/Universidade do
Porto and at COPPE Sistemas/UFRJ. Its Prolog engine is based in the WAM
(Warren Abstract Machine), with several optimizations for better performance.
YAP follows the Edinburgh tradition, and is largely compatible with the ISO-
Prolog standard and with Quintus and SICStus Prolog.

WWW: http://yap.sourceforge.net/