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2. Rough Sets: Theoretical Aspects of Reasoning about Data;Pawlak,1991
3. Interpreting Fuzzy Membership Functions in the Theory of Rough Sets;Yao,2000
4. The use of rough sets and fuzzy sets in MCDM;Greco,1999
5. Rough set approach to incomplete information systems;Kryszkiewicz;Inform. Sci.,1998