Definition:Exterior (Topology)

Definition
Let $T$ be a topological space.

Let $H \subseteq T$.

The exterior of $H$ is the complement of the closure of $H$ in $T$.

Alternatively, the exterior of $H$ is the interior of the complement of $H$ in $T$.

It can be denoted:
 * $\operatorname{Ext} \left({H}\right)$
 * $H^e$

Also see

 * Equivalence of Definitions of Exterior