## The lower and upper approximations in a fuzzy group.(English)Zbl 0878.20050

Summary: We introduce the notion of a rough subgroup with respect to a normal subgroup of a group, and give some properties of the lower and the upper approximations in a group. We also discuss a rough subgroup with respect to a $$t$$-level subset of a fuzzy normal subgroup.

### MSC:

 20N25 Fuzzy groups 20E07 Subgroup theorems; subgroup growth
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### References:

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