1) PAWLAK Z. Rough Sets-Theoretical Aspects of Reasoning about Data. Kluwer Acad. Pub.. (1991)
2) YAO Y. Y. Generalization of rough sets using modal logics. Intelligent Automation and Soft Computing. (1996) vol.2, no.2, p.103-120.
3) INUIGUCHI M. On rough sets under generalized equivalence relations. Bulletin of International Rough Set Society : Proceedings of RSTGC 2001. (2001) vol.5, no.1/2, p.167-171.
4) NAKAMURA A. Fuzzy rough sets. Note on Multiple-Valued Logic in Japan. (1988) vol.9, no.8, p.1-8.
5) RADZIKOWSKA A. M. Fuzzy rough sets revisited. Proceedings of EUFIT'99, Aachen. (1999)