▾ Set of symbols
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▾ Topological space
Open set
Formulation 0
Let $T = (X, \mathcal{T})$ be a D1106: Topological space.
A D11: Set $U \subseteq X$ is open in $T$ if and only if \begin{equation} U \in \mathcal{T} \end{equation}
Dual definition
» Closed set
Child definitions
» D98: Closed set
Results
» R293: Open set less closed set is open
» R3946: Interior is an open set
» R3944: Open set iff equal to interior