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