ThmDex – An index of mathematical definitions, results, and conjectures.
Result R3945 on D519: Set interior
Set is a superset to its interior
Formulation 0
Let $T = (X, \mathcal{T})$ be a D1106: Topological space such that
(i) $E \subseteq X$ is a D78: Subset of $X$
Then \begin{equation} \text{int} \langle E \rangle \subseteq E \end{equation}
Proofs
Proof 0
Let $T = (X, \mathcal{T})$ be a D1106: Topological space such that
(i) $E \subseteq X$ is a D78: Subset of $X$
By definition \begin{equation} \text{int} \langle E \rangle : = \bigcup \{ U \in \mathcal{T} : U \subseteq E \} \end{equation} Since every set in the union $\text{int} \langle E \rangle$ is required to be contained in $E$, then result R4152: implies the inclusion $\text{int} \langle E \rangle \subseteq E$, as claimed. $\square$