Strongly equivalent logic programs

  • Authors:

  • Vladimir Lifschitz;David Pearce;Agustín Valverde

  • Affiliations:

  • University of Texas at Austin, Austin;European Commission, Brussels, Belgium;University of Málaga, Málaga, Spain

  • Venue:
  • ACM Transactions on Computational Logic (TOCL) - Special issue devoted to Robert A. Kowalski
  • Year:
  • 2001

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Abstract

A logic program P1 is said to be equivalent to a logic program P2 in the sense of the answer set semantics if P1 and P2 have the same answer sets. We are interested in the following stronger condition: for every logic program, P, P1, ∪ P has the same answer sets as P2 ∪ P. The study of strong equivalence is important, because we learn from it how one can simplify a part of a logic program without looking at the rest of it. The main theorem shows that the verification of strong equivalence can be accomplished by cheching the equivalence of formulas in a monotonic logic, called the logic of here-and-there, which is intermediate between classical logic and intuitionistic logic.