Hard Satisfiable Formulas for Splittings by Linear Combinations

Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 10491)


Itsykson and Sokolov in 2014 introduced the class of \(\mathrm {DPLL}(\oplus )\) algorithms that solve Boolean satisfiability problem using the splitting by linear combinations of variables modulo 2. This class extends the class of \(\mathrm {DPLL}\) algorithms that split by variables. \(\mathrm {DPLL}(\oplus )\) algorithms solve in polynomial time systems of linear equations modulo 2 that are hard for \(\mathrm {DPLL}\), \(\mathrm {PPSZ}\) and \(\mathrm {CDCL}\) algorithms. Itsykson and Sokolov have proved first exponential lower bounds for \(\mathrm {DPLL}(\oplus )\) algorithms on unsatisfiable formulas.

In this paper we consider a subclass of \(\mathrm {DPLL}(\oplus )\) algorithms that arbitrary choose a linear form for splitting and randomly (with equal probabilities) choose a value to investigate first; we call such algorithms drunken \(\mathrm {DPLL}(\oplus )\). We give a construction of a family of satisfiable CNF formulas \(\varPsi _n\) of size \(\mathrm {poly}(n)\) such that any drunken \(\mathrm {DPLL}(\oplus )\) algorithm with probability at least \(1 - 2^{-\varOmega (n)}\) runs at least \(2^{\varOmega (n)}\) steps on \(\varPsi _n\); thus we solve an open question stated in the paper [12]. This lower bound extends the result of Alekhnovich, Hirsch and Itsykson [1] from drunken \(\mathrm {DPLL}\) to drunken \(\mathrm {DPLL}(\oplus )\).



The authors are grateful to Dmitry Sokolov for fruitful discussions.


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Authors and Affiliations

  1. 1.Steklov Institute of MathematicsSaint PetersburgRussia

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