<mathematics> A relation R on a set A which is a partial ordering; i.e. it is reflexive (xRx), transitive (xRyRz => xRz) and antisymmetric (xRyRx => x=y) and for any two elements x and y in A, either x R y or y R x.
See also equivalence relation, well-ordered.
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Nearby terms: total function « totally ordered « totally ordered set « total ordering » toto » touchpad » touch screen