1. A. Kandel, X.T. Peng, Z.Q. Cao, P.Z. Wang, Representation of concepts by factor spaces, in: Proc. of the Third Int. Fuzzy Systems Association (IFSA) Congress, Seattle, WA (August 6–11), 1989, pp. 145–148
2. B. De Baets, M. Gupta, E.E. Kerre, Expert knowledge representation by means of piecewise linear fuzzy quantities, in: Proc. of the Third Int. Fuzzy Systems Association Congress, 1989, Seattle, USA, pp. 618–621
3. B. Everitt, Cluster Analysis, Social Science Research Council, 1974
4. Neural Networks and Fuzzy Systems;Kosko,1992
5. Introduction to Fuzzy Sets;Luo,1989