Let $T = (X, \mathcal{T})$ be a D1106: Topological space such that

(i)	$E \subseteq X$ is a D78: Subset of $X$

The interior of $E$ in $T$ is the D11: Set \begin{equation} \text{int}_T \langle E \rangle : = \bigcup \{ U \in \mathcal{T} : U \subseteq E \} \end{equation}