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 $T$.

$\blacksquare$


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