An Algorithm to Evaluate Quanti ed Boolean Formulae

The high computational complexity of advanced reasoning tasks such as belief revision and planning calls for eecient and reliable algorithms for reasoning problems harder than NP. In this paper we propose Evaluate , an algorithm for evaluating Quantiied Boolean Formulae, a language that extends propositional logic in a way such that many advanced forms of propo-sitional reasoning, e.g., reasoning about knowledge, can be easily formulated as evaluation of a QBF. Algorithms for evaluation of QBFs are suitable for the experimental analysis on a wide range of complexity classes, a property not easily found in other formalisms. Evaluate is based on a generalization of the Davis-Putnam procedure for SAT, and is guaranteed to work in polynomial space. Before presenting Evaluate , we discuss all the abstract properties of QBFs that we singled out to make the algorithm more ee-cient. We also brieey mention the main results of the experimental analysis, which is reported elsewhere.