1. Lecture Notes in Computer Science;S Abiteboul,2006
2. Baader, F., Brandt, S., Lutz, C.: Pushing the EL. In: Proceedings of the IJCAI 2005. Morgan Kaufmann Publishers (2005)
3. Baader, F., Calvanese, D., McGuinness, D.L., Nardi, D., Patel-Schneider, P.F. (eds.): The Description Logic Handbook: Theory, Implementation, and Applications, 2nd edn. Cambridge University Press, Cambridge (2007)
4. Beigel, R., Nick, R., Spielman, D.A.: PP Is closed under intersection. J. Comput. Syst. Sci. 50(2), 191–202 (1995)
5. Bienvenu, M., Ortiz, M., Šimkus, M., Xiao, G.: Tractable queries for lightweight description logics. In: Proceedings of the IJCAI 2013. AAAI (2013)