, Volume 9, Issue 3-4, pp 387-400

Logic programs with exceptions

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We extend logic programming to deal with default reasoning by allowing the explicit representation of exceptions in addition to general rules. To formalise this extension, we modify the answer set semantics of Gelfond and Lifschitz, which allows both classical negation and negation as failure.

We also propose a transformation which eliminates exceptions by using negation by failure. The transformed program can be implemented by standard logic programming methods, such as SLDNF. The explicit representation of rules and exceptions has the virtue of greater naturalness of expression. The transformed program, however, is easier to implement.

This paper is a revised version of the paper presented at the Seventh International Conference on Logic Programming, 1990, Jerusalem.