Joseph Y. Halpern, Leandro Chaves Rêgo. Characterizing the NP-PSPACE Gap in the Satisfiability Problem for Modal Logic. In Manuela M. Veloso, editor, IJCAI 2007, Proceedings of the 20th International Joint Conference on Artificial Intelligence, Hyderabad, India, January 6-12, 2007. pages 2306-2311, 2007. [doi]
Abstract is missing.