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. (1995-02-16)