Read-Once Resolutions in Horn Formulas

  • Hans Kleine Büning
  • P. Wojciechowski
  • K. SubramaniEmail author
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 11458)


In this paper, we discuss the computational complexity of Read-once resolution (ROR) with respect to Horn formulas. Recall that a Horn formula is a boolean formula in conjunctive normal form (CNF), such that each clause has at most one positive literal. Horn formulas find applications in a number of domains such as program verification and logic programming. It is well-known that deduction in ProLog is based on unification, which in turn is based on resolution and instantiation. Resolution is a sound and complete procedure to check whether a boolean formula in CNF is satisfiable. Although inefficient in general, resolution has been used widely in theorem provers, on account of its simplicity and ease of implementation. This paper focuses on two variants of resolution, viz., Read-once resolution and Unit Read-once resolution (UROR). Both these variants are sound, but incomplete. In this paper, the goal is to check for the existence of proofs (refutations) of Horn formulas under these variants. We also discuss the computational complexity of determining optimal length proofs where appropriate.


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Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  • Hans Kleine Büning
    • 1
  • P. Wojciechowski
    • 2
  • K. Subramani
    • 2
    Email author
  1. 1.Computer Science InstituteUniversity of PaderbornPaderbornGermany
  2. 2.LDCSEEWest Virginia UniversityMorgantownUSA

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