Solving Disjunctive/Conjunctive Boolean Equation Systems with Alternating Fixed Points

This paper presents a technique for the resolution of alternating disjunctive/conjunctive boolean equation systems. The technique can be used to solve various verification problems on finite-state concurrent systems, by encoding the problems as boolean equation systems and determining their local solutions. The main contribution of this paper is that a recent resolution technique from [13] for disjunctive/conjunctive boolean equation systems is extended to the more general disjunctive/conjunctive forms with alternation. Our technique has the time complexity O(m+n2), where m is the number of alternation free variables occurring in the equation system and n the number of alternating variables. We found that many µ-calculus formulas with alternating fixed points occurring in the literature can be encoded as boolean equation systems of disjunctive/conjunctive forms. Practical experiments show that we can verify alternating formulas on state spaces that are orders of magnitudes larger than reported up till now.