Reflexive Closure is Reflexive
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Theorem
Let $\RR$ be a relation on a set $S$.
Then $\RR^=$, the reflexive closure of $\RR$, is reflexive.
Proof
Recall the definition of reflexive closure:
- $\RR^= := \RR \cup \Delta_S$
From Set is Subset of Union:
- $\Delta_S \subseteq \RR^=$
The result follows directly from Relation Contains Diagonal Relation iff Reflexive.
$\blacksquare$
Sources
- 1971: Robert H. Kasriel: Undergraduate Topology ... (previous) ... (next): $\S 1.19$: Some Important Properties of Relations: Exercise $2$