Article

# Hyperequivalence of logic programs with respect to supported models.

Annals of Mathematics and Artificial Intelligence (Impact Factor: 0.2). 01/2008; 53:331-365. DOI: 10.1007/s10472-009-9119-8

Source: DBLP

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**ABSTRACT:**Equivalence and generality relations over logic programs have been proposed in answer set programming to semantically compare information contents of logic programs. In this paper, we overview previous relations of answer set programs, and propose a general framework that subsumes previous relations. The proposed framework allows us to compare programs possibly having non-minimal answer sets as well as to explore new relations between programs. Such new relations include relativized variants of generality relations over logic programs. By selecting contexts for comparison, the proposed framework can represent weak, strong and uniform variants of generality, inclusion and equivalence relations. These new relations can be applied to comparison of abductive logic programs and coordination of multiple answer set programs.04/2011: pages 91-110; - [Show abstract] [Hide abstract]

**ABSTRACT:**Over the years, the stable-model semantics has gained a position of the correct (two-valued) interpretation of default negation in programs. However, for programs with aggregates (constraints), the stable-model semantics, in its broadly accepted generalization stemming from the work by Pearce, Ferraris and Lifschitz, has a competitor: the semantics proposed by Faber, Leone and Pfeifer, which seems to be essentially different. Our goal is to explain the relationship between the two semantics. Pearce, Ferraris and Lifschitz's extension of the stable-model semantics is best viewed in the setting of arbitrary propositional theories. We propose here an extension of the Faber–Leone–Pfeifer semantics, or FLP semantics, for short, to the full propositional language, which reveals both common threads and differences between the FLP and stable-model semantics. We use our characterizations of FLP-stable models to derive corresponding results on strong equivalence and on normal forms of theories under the FLP semantics. We apply a similar approach to define supported models for arbitrary propositional theories, and to study their properties.Artif. Intell. 01/2010; 174:1285-1306. - [Show abstract] [Hide abstract]

**ABSTRACT:**Different notions of equivalence, such as the prominent notions of strong and uniform equivalence, have been studied in Answer-Set Programming, mainly for the purpose of identifying programs that can serve as substitutes without altering the semantics, for instance in program optimization. Such semantic comparisons are usually characterized by various selections of models in the logic of Here-and-There (HT). For uniform equivalence however, correct characterizations in terms of HT-models can only be obtained for finite theories, respectively programs. In this article, we show that a selection of countermodels in HT captures uniform equivalence also for infinite theories. This result is turned into coherent characterizations of the different notions of equivalence by countermodels, as well as by a mixture of HT-models and countermodels (so-called equivalence interpretations). Moreover, we generalize the so-called notion of relativized hyperequivalence for programs to propositional theories, and apply the same methodology in order to obtain a semantic characterization which is amenable to infinite settings. This allows for a lifting of the results to first-order theories under a very general semantics given in terms of a quantified version of HT. We thus obtain a general framework for the study of various notions of equivalence for theories under answer-set semantics. Moreover, we prove an expedient property that allows for a simplified treatment of extended signatures, and provide further results for non-ground logic programs. In particular, uniform equivalence coincides under open and ordinary answer-set semantics, and for finite non-ground programs under these semantics, also the usual characterization of uniform equivalence in terms of maximal and total HT-models of the grounding is correct, even for infinite domains, when corresponding ground programs are infinite. Comment: 32 pages; to appear in Theory and Practice of Logic Programming (TPLP)Theory and Practice of Logic Programming 06/2010; · 0.29 Impact Factor

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## Miroslaw Truszczynski |