1. Baldwin J.F.: Support logic programming. International Journal of Intelligent Systems 1:73–104, (1986).
2. Chatalic P., Froidevaux, C.: Graded logics: a framework for uncertain and defeasible knowledge. in Methodologies for Intelligent Systems (eds) Z.W. Ras, M. Zemankova, Lecture Notes in Artificial Intelligence, Vol. 542, Springer Verlag, (1991).
3. Da Costa N.C.A.: Calculus propositionnels pour les systèmes formels inconsistants. Compte Rendu Acad. des Sciences (Paris), 257:3790–3792, (1963).
4. Dubois D., Lang. J, Prade, H.: Theorem-proving under uncertainty A possibilistic theory-based approach. Proceedings of 10th International Joint Conference on Artificial Intelligence, Milano, Italy, 984–986, (1987).
5. Dubois D., Lang, J., Prade, H.: Automated reasoning using possibilistic logic: semantics, belief revision, variable certainty weights. Proceedings 5th Workshop on Uncertainty in AI, Windsor, Ont., 81–87, (1989).