STABLE MODELS ARE GENERATED BY A STABLE CHAIN

We propose a general preference criterion selecting the ''intended'' m odels of generalized logic programs which: 1) is a conservative extens ion of the stable model semantics for normal logic programs of [2], 2) is very close to the answer set semantics of [4] for disjunctive logi c programs, and 3) allows for arbitrary formulas in the body and in th e head of a rule, i.e., does not depend on the presence of any specifi c connective, such as negation(-as-failure) or on any specific syntax of rules. Our preference criterion defines a model of a program as int ended if it is generated by a stable chain. We show that stable models and answer sets are generated by a stable chain of length less than o r equal to omega. (C) Elsevier Science Inc., 1997