Two SAT solvers for solving quantified Boolean formulas with an arbitrary number of quantifier alternations
Sprache des Titels:
Englisch
Original Kurzfassung:
In recent years, expansion-based techniques have been shown to be very powerful in theory
and practice for solving quantified Boolean formulas (QBF), the extension of propositional
formulas with existential and universal quantifiers over Boolean variables. Such approaches
partially expand one type of variable (either existential or universal) for obtaining a proposi-
tional abstraction of the QBF. If this formula is false, the truth value of the QBF is decided,
otherwise further refinement steps are necessary. Classically, expansion-based solvers pro-
cess the given formula quantifier-block wise and use one SAT solver per quantifier block. In
this paper, we present a novel algorithm for expansion-based QBF solving that deals with the
whole quantifier prefix at once. Hence recursive applications of the expansion principle are
avoided and only two incremental SAT solvers are required. While our algorithm is naturally
based on the ?Exp+Res calculus that is the formal foundation of expansion-based solving,
it is conceptually simpler than present recursive approaches. Experiments indicate that theFormal Methods in System Design
performance of our simple approach is comparable with the state of the art of QBF solving,
especially in combination with other solving techniques.
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