@inproceedings{ijcai2007p371,
  title     = {Characterizing the NP-PSPACE Gap in the Satisfiability Problem for Modal Logic},
  author    = {Halpern, Joseph Y. and Rêgo, Leandro Chaves},
  booktitle = {Proceedings of the Twentieth International Joint Conference on
               Artificial Intelligence, {IJCAI-07}},
  publisher = {International Joint Conferences on Artificial Intelligence},
  editor    = {Ramon López de Mántaras},
  pages     = {2306--2310},
  year      = {2007},
  url       = {https://ijcai.org/proceedings/2007/371},
}