Let $T = (X, \mathcal{T})$ be a D1106: Topological space such that
(i) | $E \subseteq X$ is a D78: Subset |
(ii) | $\mathsf{int}(E)$ is the D519: Set interior of $E$ in $T$ |
Then
\begin{equation}
\mathsf{int}(E) \in \mathcal{T}
\end{equation}