Definition:Reflexive Transitive Closure/Transitive Closure of Reflexive Closure

Definition
Let $\mathcal R$ be a relation on a set $S$. The reflexive transitive closure of $\mathcal R$ is denoted $\mathcal R^*$, and is defined as the transitive closure of the reflexive closure of $\mathcal R$:
 * $\mathcal R^* = \left({\mathcal R^=}\right)^+$