Union of Reflexive Relations is Reflexive

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

Proof
Let $$\mathcal{R}_1$$ and $$\mathcal{R}_2$$ be reflexive relations on a set $$S$$.

From Reflexive contains Diagonal Relation, we have that:
 * $$\Delta_S \subseteq \mathcal{R}_1$$;
 * $$\Delta_S \subseteq \mathcal{R}_2$$.

Hence from Subsets Transitive, $$\Delta_S \subseteq \mathcal{R}_1 \cup \mathcal{R}_2$$.

Hence the result, from Reflexive contains Diagonal Relation.