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Characterization of rough top equalities and rough bottom equalities. (English) Zbl 0569.68083
In Int. J. Comput. Inf. Sci. 11, 341-356 (1982; Zbl 0501.68053) the rough top equality between subsets of a finite set was introduced by the second author. In Ann. Soc. Math. Pol., Ser. IV, Fundam. Inf. 6, 289-296 (1983; Zbl 0522.68094) the rough top equality was proved by the authors to be a congruence on a certain semilattice. In this article, we characterize rough top equalities among all congruences of the mentioned semilattice. A similar result is obtained for rough bottom equalities.

68P20Information storage and retrieval
03E20Other classical set theory (logic)