# Category:Set Interiors

The interior of $H$ is the union of all subsets of $H$ which are open in $T$.
That is, the interior of $H$ is defined as:
$\displaystyle H^\circ := \bigcup_{K \mathop \in \mathbb K} K$
where $\mathbb K = \left\{{K \in \tau: K \subseteq H}\right\}$.