Closed Set in Topological Subspace/Corollary
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Theorem
Let $T = \struct{S, \tau}$ be a topological space.
Let $T' = \struct{H, \tau_H}$ be a subspace of $T$ where $H \subseteq S$.
Let $H$ be closed in $T$.
Then $V \subseteq H$ is closed in $T'$ if and only if $V$ is closed in $T$.
Proof
Let $V \subseteq H$ be closed in $T'$.
Then, from Closed Set in Topological Subspace, $V = H \cap V$ is closed in $T'$.
If $V$ is closed in $T'$ then $V = H \cap W$ where $W$ is closed in $T$.
Since $H$ is closed in $T$, it follows by Topology Defined by Closed Sets that $V$ is closed in $T$.
$\blacksquare$
Also see
Sources
- 1975: W.A. Sutherland: Introduction to Metric and Topological Spaces ... (previous) ... (next): $3$: Continuity generalized: topological spaces: $3.7$: Definitions: Corollary $3.7.7$
- 2011: John M. Lee: Introduction to Topological Manifolds (2nd ed.) ... (previous) ... (next): $\S 3$: New Spaces From Old: Subspaces