Nested expressions in logic programs

Vladimir Lifschitz, Lappoon R. Tang, Hudson Turner

Research output: Contribution to journalArticlepeer-review

236 Scopus citations


We extend the answer set semantics to a class of logic programs with nested expressions permitted in the bodies and heads of rules. These expressions are formed from literals using negation as failure, conjunction (,) and disjunction (;) that can be nested arbitrarily. Conditional expressions are introduced as abbreviations. The study of equivalent transformations of programs with nested expressions shows that any such program is equivalent to a set of disjunctive rules, possibly with negation as failure in the heads. The generalized answer set semantics is related to the Lloyd-Topor generalization of Clark's completion and to the logic of minimal belief and negation as failure.

Original languageEnglish (US)
Pages (from-to)369-389
Number of pages21
JournalAnnals of Mathematics and Artificial Intelligence
Issue number3-4
StatePublished - 1999


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