Cycle unification

  • Wolfgang Bibel
  • Steffen Hölldobler
  • Jörg Würtz
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 607)


Two-literal clauses of the form L ← R occur quite frequently in logic programs, deductive databases, and — disguised as an equation — in term rewriting systems. These clauses define a cycle if the atoms L and R are weakly unifiable, ie. if L unifies with a new variant of R. The obvious problem with cycles is to control the number of iterations through the cycle. In this paper we consider the cycle unification problem of unifying two literals G and F modulo a cycle. We review the state of the art of cycle unification and give some new results for a special type of cycles called matching cycles, ie. cycles L←R for which there exists a substitution σ such that σL=R or L=σR. Altogether, these results show how the deductive process can be efficiently controlled for special classes of cycles without losing completeness.


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Copyright information

© Springer-Verlag Berlin Heidelberg 1992

Authors and Affiliations

  • Wolfgang Bibel
    • 1
  • Steffen Hölldobler
    • 1
  • Jörg Würtz
    • 2
  1. 1.Fachgruppe Intellektik, Fachbereich Informatik, Technische Hochschule DarmstadtDarmstadtGermany
  2. 2.Deutsches Forschungszentrum für Künstliche IntelligenzSaarbrücken 11Germany

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