Union of Reflexive Relations is Reflexive

Theorem
The union of two reflexive relations is also a reflexive relation.

Proof
Let $\RR_1$ and $\RR_2$ be reflexive relations on a set $S$.

From Relation Contains Diagonal Relation iff Reflexive, we have that:
 * $\Delta_S \subseteq \RR_1$
 * $\Delta_S \subseteq \RR_2$

Hence from Subset Relation is Transitive:
 * $\Delta_S \subseteq \RR_1 \cup \RR_2$

Hence the result, by definition of reflexive relation.