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    Solving SAT for CNF formulas with a one-sided restriction on variable occurrences

    Johannsen, D. and Razgon, Igor and Wahlström, M. (2009) Solving SAT for CNF formulas with a one-sided restriction on variable occurrences. In: Kullmann, O. (ed.) Theory and Applications of Satisfiability Testing. Lecture Notes in Computer Science 5584. Berlin, Germany: Springer Verlag, pp. 80-85. ISBN 9783642027765.

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    In this paper we consider the class of boolean formulas in Conjunctive Normal Form (CNF) where for each variable all but at most d occurrences are either positive or negative. This class is a generalization of the class of CNF formulas with at most d occurrences (positive and negative) of each variable which was studied in [Wahlström, 2005]. Applying complement search [Purdom, 1984], we show that for every d there exists a constant γd<2−12d+1 such that satisfiability of a CNF formula on n variables can be checked in runtime \ensuremathO(γnd) if all but at most d occurrences of each variable are either positive or negative. We thoroughly analyze the proposed branching strategy and determine the asymptotic growth constant γ d more precisely. Finally, we show that the trivial \ensuremathO(2n) barrier of satisfiability checking can be broken even for a more general class of formulas, namely formulas where the positive or negative literals of every variable have what we will call a d–covering. To the best of our knowledge, for the considered classes of formulas there are no previous non-trivial upper bounds on the complexity of satisfiability checking.


    Item Type: Book Section
    School: Birkbeck Faculties and Schools > Faculty of Science > School of Computing and Mathematical Sciences
    Depositing User: Sarah Hall
    Date Deposited: 01 Aug 2013 15:51
    Last Modified: 09 Aug 2023 12:34


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