McCarthy's simple abnormality formalism provides a new way to paraphrase commonsense knowledge by using the word "unless", roughly called the "unless" semantics. In this paper, we first point out that the introduced inheritance cancellation axioms in this formalism may cause the semantic inconsistency problem in the paraphrases of the models obtained from circumscription and propose a simple way to resolve it. We then explore the "unless" semantics in the convention of commonsense reasoning and propose the extended answer set semantics to incorporate this new semantics in extended logic programs. It turns out that a clause in an extended logic program can be transformed into one of four other different forms based on the given information so that the conclusions will become more reasonable and the transformed programs more coherent.
Proceedings of the International Computer Symposium 1994 (ICS-94), Hsinchu, pp.491-496