Algorithms for Kleene algebra with converse
The equational theory generated by all algebras of binary relations with operations of union, composition, converse and reflexive transitive closure was studied by Bernátsky, Bloom, Ésik and Stefanescu in 1995. In particular, they obtained its decidability by using a particular automata construction. We show that deciding this equational theory is PSpacecomplete, by providing a PSpace algorithm (the problem is easily shown to be PSpacehard). We obtain other algorithms that are timeefficient in practice, despite not being PSpace. Our results use an alternative automata construction, inspired by the one from Bloom, Ésik and Stefanescu. We relate those two constructions by exhibiting a bisimulation between the resulting deterministic automata, and by showing how our construction results in more sharing between states, thus producing smaller automata.
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