▾ Set of symbols
▾ Alphabet
▾ Deduction system
▾ Theory
▾ Zermelo-Fraenkel set theory
▾ Set
▾ Subset
▾ Power set
▾ Hyperpower set sequence
▾ Hyperpower set
▾ Hypersubset
▾ Subset algebra
▾ Subset structure
▾ Topological space
▾ Set interior
Set exterior
Formulation 0
Let $T = (X, \mathcal{T})$ be a D1106: Topological space.
The exterior of $E \subseteq X$ in $T$ is the D11: Set \begin{equation} \mathsf{ext}_T(E) : = \mathsf{int}_T(X \setminus E) \end{equation}