a relation that is reflexive and transitive, but not necessarilyantisymmetric
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A preorder is a binary relation that is reflexive and transitive. Such orders may also be called quasiorders.
In mathematics, especially in order theory, preorders are binary relations such as, for example, partially ordered sets. The name quasiorder is also common for preorders. Many order theoretical definitions for partially ordered sets can be generalized to preorders, but the extra effort of generalization is rarely needed.
