1. Elements of Mathematics: General Topology;Bourbaki,1989
2. Semantic and algorithmic aspects of approximate reasoning in possibility theory;Dubois;Rapport IRIT/90-53/R,1990
3. The generalized modus ponens considered as a fuzzy relation;Hellendoorn;Fuzzy Sets and Systems,1992
4. General Topology and Homotopy Theory;James,1984
5. On modified set-operations;Kortelainen,1993