1. S. Benfehrat, D. Dubois and H. Prade, ?Representing default rules in possibilistic logic?, in Proc. of the 3rd Inter. Conf. on Principles of Knowledge Representation and Reasoning (KR'92), Cambridge, USA, 1992, edited by B. Nebel, C. Rich, and W. Swartout, Morgan & Kaufmann: San Mateo, CA, 1992, pp. 673?684.
2. A. Borning, M. Maher, A. Marindale, and M. Wilson, ?Constraint hierarchies and logic programming,? in Proc. of the Inter. Conf. on Logic Programming, Lisbon, Portugal, June 1989, pp. 149?164.
3. P. Bosc and O. Pivert, ?An approach for a hierarchical aggregation of fuzzy predicates,? in Proc. of the 2nd IEEE Inter. Conf. on Fuzzy Systems (FUZZ-IEEE'93), San Francisco, CA, March 28-April 1, 1993, pp. 1231?1236.
4. J. Bowen, R. Lai, and D. Bahler, ?Fuzzy semantics and fuzzy constraint networks,? in Proc. of the 1st IEEE Conf. on Fuzzy Systems, San Fransisco, 1992, pp. 1009?1016.
5. J. Bowen, R. Lai, and D. Bahler, ?Lexical imprecision in fuzzy constraint networks,? in Proc. of the National Conf. on Artificial Intelligence, 1992, pp. 616?620.