Trichotomy is Antireflexive
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Theorem
Let $\RR$ be a trichotomy.
Then $\RR$ is an antireflexive relation.
Proof
Let $\RR$ be a trichotomy on a set $S$.
Let $x \in S$.
By definition of a trichotomy, for all $a, b \in S$, either:
- $a \mathrel \RR b$
- $a = b$
- $b \mathrel \RR a$
As $x = x$ it follows directly that $x \not < x$.
Hence the result by definition of antireflexive relation.
$\blacksquare$