\begin{definition}[Definition:Reflexive Closure/Smallest Reflexive Superset]
Let $\RR$ be a relation on a set $S$.
The '''reflexive closure''' of $\RR$ is defined as the smallest reflexive relation on $S$ that contains $\RR$ as a subset.
The '''reflexive closure''' of $\RR$ is denoted $\RR^=$.
\end{definition}