Symmetry Reduced Model Checking for B

Symmetry reduction is a technique that can help alleviate the problem of state space explosion in model checking. The idea is to verify only a subset of states from each class (orbit) of symmetric states. This paper presents a framework for symmetry reduced model checking of B machines, which verifies a unique representative from each orbit. Symmetries are induced by the deferred set; a key component of the B language. This contrasts with strategies that require the introduction of a special data type into a language, to indicate symmetry. An extended version of the graph isomorphism program, nauty, is used to detect symmetries, and the symmetry reduction package has been integrated into the PROB model checker. Relevant algorithms are presented, and experimental results illustrate the effectiveness of the method, where exponential speedups are sometimes possible.