Definition:Reflexive Transitive Closure/Transitive Closure of Reflexive Closure

Definition
Let $\RR$ be a relation on a set $S$. The reflexive transitive closure of $\RR$ is denoted $\RR^*$, and is defined as the transitive closure of the reflexive closure of $\RR$:
 * $\RR^* = \paren {\RR^=}^+$