Let $T = (X, \mathcal{T})$ be a D1106: Topological space such that
(i) | $U \subseteq X$ is a D78: Subset |
Then $U \in \mathcal{T}$ if and only if
\begin{equation}
\mathsf{int} (U) = U
\end{equation}
(i) | $U \subseteq X$ is a D78: Subset |