ThmDex – An index of mathematical definitions, results, and conjectures.
Result R3946 on D97: Open set
Interior is an open set
Formulation 0
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}