Definition 1. The identity on a set $X$ is the binary relation
\[\id_X = \{(x, x) : x \in X\}.\]Note. For any set $X$, $\id_X$ is also a function (the identity function).
Pub Feb 21, 2026 Up Jun 28, 2026
Definition 1. The identity on a set $X$ is the binary relation
\[\id_X = \{(x, x) : x \in X\}.\]Note. For any set $X$, $\id_X$ is also a function (the identity function).