Definitions for "Equivalence relation"
A 2-place set-theoretic relation R that is reflexive, symmetric, and transitive. I. e. xRx, xRy if and only if yRx, and xRy plus yRz imply xRz. An equivalence relation on a set partitions the set into disjoint equivalence classes (subsets of elements which are all equivalent to each other).
a binary relation that is reflexive, transitive, and symmetric
a reflexive, symmetrical, and transitive relation