Definition:Reflexive Relation/Class Theory

Definition
Let $V$ be a basic universe.

Let $\RR \subseteq V \times V$ be a relation in $V$.

$\RR$ is reflexive :


 * $\forall x \in \Field \RR: \tuple {x, x} \in \RR$

where $\Field \RR$ denotes the field of $\RR$.