1. Biswas R, Nanda S (1994) Rough groups and rough subgroups. Bull Polish Acad Sci Math 42:251–254
2. Bonikowaski Z (1995) Algebraic structures of rough sets. In: Ziako WP (ed) Rough sets fuzzy sets, and knowledge discovery. Springer-Verlag, Berlin
3. Davvaz B (2004) Roughness in rings. Inf Sci 164:147–163
4. Davvaz B (2006) Roughness based on fuzzy ideals. Inf Sci 176:2417–2437
5. Davvaz B, Dudek WA (2009) Fuzzy n-ary groups as a generalization of Rosenfeld’s fuzzy groups. J. Multi-Valued Logic Soft Comput. 15:451–469