Yap is a high-performance Prolog compiler developed at LIACC, Universidade do Porto. Its Prolog engine is based on the WAM (Warren Abstract Machine), with several optimizations for better performance, and achieves performance comparable or exceeding that of commercial Prolog systems. Yap is largely compatible with the major Edinburgh Prolog systems, and has been ported to most 32-bit and 64-bit Unix based platforms. A Windows port is also available. License: Artistic License Changes: Numerous major enhancements.

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