Definition:Relation Segment

Definition
Let $X$ be a set.

Let $\RR$ be a relation on $X$.

Let $x \in X$.

Then the $\RR$-segment of $x$, denoted by $x^\RR$, is defined by:
 * $x^\RR := \set {y \in X: \tuple {y, x} \in \RR}$