The aim of this paper is to analyze Approximate Reasoning (AR) through
extensionality with respect to the natural T-indistinguishability ope
rator, by considering the indistinguishability level between fuzzy set
s as a formal measure of its degree of similarity, resemblance or clos
eness, having in all these terms an intuitive meaning. (C) 1998 Elsevi
er Science Inc. All rights reserved.