Quantifier rewriting and equivalence models for quantified horn formulas

  • Authors:
  • Uwe Bubeck;Hans Kleine Büning;Xishun Zhao

  • Affiliations:
  • International Graduate School Dynamic Intelligent Systems, Universität Paderborn, Paderborn, Germany;Department of Computer Science, Universität Paderborn, Paderborn, Germany;Institute of Logic and Cognition, Zhongshan University, Guangzhou, P.R. China

  • Venue:
  • SAT'05 Proceedings of the 8th international conference on Theory and Applications of Satisfiability Testing
  • Year:
  • 2005

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Abstract

In this paper, quantified Horn formulas with free variables (QHORN*) are investigated. The main result is that any quantified Horn formula Φ of length |Φ| with free variables, |∀| universal quantifiers and an arbitrary number of existential quantifiers can be transformed into an equivalent formula of length O(|∀| ·|Φ|) which contains only existential quantifiers. Moreover, it is shown that quantified Horn formulas with free variables have equivalence models where every existential quantifier is associated with a monotone Boolean function. The results allow a simple representation of quantified Horn formulas as purely existentially quantified Horn formulas (∃HORN*). An application described in the paper is to solve QHORN*-SAT in O(|∀| ·|Φ|) by using this transformation in combination with a linear-time satisfiability checker for propositional Horn formulas.