1. 1) BEZDEK J. C. Fuzzy partitions and relations ; An axiomatic basis for clustering. Fuzzy Sets and Systems. (1978) vol.1, p.112-127.
2. 2) CAIANIELLO E. R. C-calculus and fuzzy sets. Proc. 1st Napoli Meeting on the Mathematics of Fuzzy Systems. (1984) p.29-33.
3. 3) CHELLAS B. F. Modal Logic, an Introduction. Cambridge Univ. Press. (1980)
4. 4) DUBOIS D. Possibility Theory : An Approach to Computerized Processing of Uncertainty. Plenum Press. (1988)
5. 5) DUBOIS D. Putting rough sets and fuzzy sets together. Intelligent Decision Support. Kluwer Acad. Publ.. (1992) p.203-232.