The Alternating Semantics for Default Theories and Logic Programs
نویسنده
چکیده
In this paper we propose a semantics for default theories, based on van Gelder's alternating xpoint theory. The distinct feature of this semantics is its preservation of Reiter's semantics when a default theory is not considered \problematic" under Reiter's semantics. Diierences arise only when a default theory has no extensions, or has only \biased extensions" under Reiter's semantics. This feature allows skeptical reasoning in Reiter's logic to be properly preserved in the new semantics. By the familiar, natural translation from logic programs to default theories, the semantics proposed for default theories provides a natural extension to the stable model semantics of normal logic programs.
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