<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.
total function « totally ordered « totally ordered
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