Definition:Reflexive Closure

Definition
Let $\mathcal R$ be a relation on a set $S$.

The reflexive closure of $\mathcal R$ is denoted $\mathcal R^=$, and is defined as:


 * $\mathcal R^= := \left\{{\left({x, x}\right): x \in S}\right\} \cup \mathcal R$

From Union Smallest: General Result, it follows that $\mathcal R^=$ is the smallest reflexive relation on $S$ which contains $\mathcal R$.

It also follows from Intersection with Subset is Subset‎ that $\mathcal R^=$ is the intersection of all reflexive relations which contain $\mathcal R$.

Thus if $\mathcal R$ is reflexive, then $\mathcal R = \mathcal R^=$.