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Ideas of Seymour Lipschutz, by Text

[American, fl. 1998, Professor of Mathematics at Temple University.]

1998 Set Theory and related topics (2nd ed)
3.9 p.73 Equivalence relations are reflexive, symmetric and transitive, and classify similar objects
     Full Idea: A relation R on a non-empty set S is an equivalence relation if it is reflexive (for each member a, aRa), symmetric (if aRb, then bRa), and transitive (aRb and bRc, so aRc). It tries to classify objects that are in some way 'alike'.
     From: Seymour Lipschutz (Set Theory and related topics (2nd ed) [1998], 3.9)
     A reaction: So this is an attempt to formalise the common sense notion of seeing that two things have something in common. Presumably a 'way' of being alike is going to be a property or a part