Deciding regular grammar logics with converse through first-order logic
Résumé
We provide a simple translation of the satisfiability problem for regular grammar logics with converse into GF 2 , which is the intersection of the guarded fragment and the 2-variable fragment of first-order logic. This translation is theoretically interesting because it translates modal logics with certain frame conditions into first-order logic, without explicitly expressing the frame conditions. The class of regular grammar logics includes numerous logics from quite different application domains. The notion of regularity is directly related to the frame condition of the logics. A consequence of the translation is that the general satisfiability problem for every regular grammar logics with converse is in EXPTIME. This extends a previous result of the first author for grammar logics without converse. Using the same method, we show that some other modal logics can be naturally translated into GF2 , including nominal tense logics and intuitionistic logic. In our view, the results in this paper show that the natural first-order fragment corresponding to regular grammar logics is simply GF 2 without extra machinery such as fixed point-operators.