During the past 40 years of fuzzy research at the Fuzziness and Uncertainty Modeling research unit of Ghent University several axiomatic systems and characterizations have been introduced. In this paper we highlight some of them. The main purpose of this paper consists of an invitation to continue research on these first attempts to axiomatize important concepts and systems in fuzzy set theory. Currently, these attempts are spread over many journals; with this paper they are now collected in a neat overview. In the literature, many axiom systems have been introduced, but as far as we know the axiomatic system of Huntington concerning a Boolean algebra has been the only one where the axioms have been proven independent. Another line of further research could be with respect to the simplification of these systems, in discovering redundancies between the axioms. Keywords: fuzzy set; fuzzy preference structure; fuzzy topology
OverviewWe start with the characterization of a Chang fuzzy topology by means of a preassigned operation such as an interior operator. In Section 3 we dwell upon the separation axioms in Chang fuzzy topological spaces and refer to dependencies between the different fuzzy separation axioms. In Section 4 a fuzzy extension of the well-known Armstrong axioms in a fuzzy relational database is given. A lot of work has been done on the characterization of a fuzzy preference structure. Some results are repeated in Section 5. In the next section a characterization is given of lattices that are needed to establish the equivalence between Goguen's L-fuzzy sets and Gentilhomme's L-flou sets, leading to the introduction of the kite-tail lattices. We also dwell upon the modifications of the condition that sometimes appear in the literature. Section 7 summarizes the work on the axiomatization of the ordering of fuzzy quantities, in particular fuzzy numbers. In the next section some axioms are introduced for a defuzzification technique in order to transform a fuzzy set into a single element of the underlying universe. The concept of a fuzzy implication is important from a theoretical as well as a practical point of view. In Section 9 we describe the extension of Smets-Magrez axioms for a fuzzy implication. Finally Section 10 treats the axiomatization of a triangle algebra.
On the Characterization of a Chang Fuzzy Topology by Means of Preassigned OperationsPerhaps general topology has been the first mathematical structure that has been fuzzified. Already in 1968, three years after the publication of Zadeh's seminal paper "Fuzzy Sets" [1], Chang's paper "Fuzzy Topological Spaces" [2] appeared in JMAA. A fuzzy topology on a set X was defined as a class T of fuzzy sets satisfying the straightforward fuzzifications of the classical axioms for a fuzzy topology: