1. Baader, F., 1991, ?Augmenting concept languages by transitive closure of roles: An alternative to terminological cycles,?Proceedings of the 12th International Joint Conference on Artificial Intelligence, pp. 446?451, Sydney, Australia.
2. Blackburn, P. and Spaan, E., 1992, ?A modal perspective on the computational complexity of attribute value grammar,? Logic Group Preprint Series No. 77, Department of Philosophy, Utrecht University, The Netherlands.
3. Boone, W. W., 1959, ?The word problem,?Ann. of Mat. 70, 207?265.
4. Brachman, R. J. and Schmolze, J. G., 1985, ?An overview of the KL-ONE knowledge representation system.?Cognitive Science,9(2), 171?216.
5. Goldblatt, R., 1987,Logics of Time and Computation, CSLI Lecture Notes 7. Center for the Study of Language and Information, Stanford University, California, USA.