Stable Models Are Generated by a Stable Chain

We propose a general preference criterion selecting thèintended' models of generalized logic programs which a) is a conservative extension of the stable model semantics for normal logic programs of GL88], b) is very close to the answer set semantics of GL91] for disjunctive logic programs, and c) allows for arbitrary formulas in the body and in the head of a rule, i.e. does not depend on the presence of any speciic connective, such as negation(as failure), nor on any speciic syntax of rules. Our preference criterion deenes a model of a program as intended if it is generated by a stable chain. We show that stable models and answer sets are generated by a stable chain of length !.