Definition:Trichotomy

Definition
Let $S$ be a set.

A trichotomy on $S$ is a relation $\mathcal R$ on $S$ such that for every pair of elements $a, b \in S$, exactly one of the following three conditions applies:


 * $a \mathop {\mathcal R} b$
 * $a = b$
 * $b \mathop {\mathcal R} a$

Example
A classic example of a trichotomy is the standard less than ordering on the set of real numbers.

Also see

 * Trichotomy Law: an ordering $\prec$ is a strict total ordering iff $\prec$ is a trichotomy.