Symmetric and Antisymmetric Relation is Transitive
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Theorem
Let $S$ be a set.
Let $\RR \subseteq S \times S$ be a relation in $S$ which is both symmetric and antisymmetric.
Then $\RR$ is transitive.
Proof
Let $\tuple {x, y}, \tuple {y, z} \in \RR$.
By Relation is Symmetric and Antisymmetric iff Coreflexive:
- $x = y, y = z$
and so trivially:
- $\tuple {x, z} = \tuple {x, x} \in \RR$
Thus $\RR$ is transitive.
$\blacksquare$
Sources
- 1965: E.J. Lemmon: Beginning Logic ... (previous) ... (next): Chapter $4$: The Predicate Calculus $2$: $5$ Properties of Relations: Exercise $5$