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:


 * $a \; \mathcal R \; b$
 * $a = b$
 * $b \; \mathcal R \; a$

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

From the Trichotomy Law, we have that an ordering $\prec$ is a strict total ordering iff $\prec$ is a trichotomy.