In this work we present additional results related to the property of strongequivalence of logic programs. This property asserts that two programs sharethe same set of stable models, even under the addition of new rules. As shownin a recent work by Lifschitz, Pearce and Valverde, strong equivalence can besimply reduced to equivalence in the logic of Here-and-There (HT). In thispaper we provide two alternatives respectively based on classical logic and3-valued logic. The former is applicable to general rules, but not for nestedexpressions, whereas the latter is applicable for nested expressions but, whenmoving to an unrestricted syntax, it generally yields different results fromHT.
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