Adding forward chaining and truth maintenance to Prolog

A description is given of P_fc, a simple package which supplies a forward chaining facility in Prolog. P _fc is intended to be used in conjunction with ordinary Prolog programs, allowing the programmer to decide whether to encode a rule as a forward-chaining P_fc rule or a backward-chaining Prolog one. Like other programming languages, P_fc programs have a declarative interpretation as well as a clear and predictable procedural one. A truth maintenance system built into P _fc system maintains consistency and makes derivations available for applications. Finally, P_fc is designed to be relatively efficient and unobtrusive