1. Rough sets;Pawlak;International Journal of Information and Computer Science,1982
2. Rough Sets: Theoretical Aspects of Reasoning about Data;Pawlak,1991
3. Theories of Vagueness;Keefe,2000
4. Rough sets: an approach to vagueness;Pawlak,2005
5. Vagueness;Russell;Australasian Journal of Philosophy and Psychology,1923