Is this a sufficient condition for a subset of a topological space to be closed?
97373
Is whether a set is closed or not a local property?
36237
Closed set mapped to itself in a compact Hausdorff space
97951
Is the void set (∅) a proper subset of every set?
127900
Interior of closure of open set in topological space
78399
In $T_1$ space, all singleton sets are closed?
105445
Are the rationals a closed or open set in $\mathbb{R}$?
146146
Proof that a closed subset of a compact space is a compact space
84512
The preimage of continuous function on a closed set is closed.
21114
$S=\{(n,{1\over n}):n\in\mathbb{N}\}$ is closed in $X$?
110744
How to prove that a compact set in a Hausdorff topological space is closed?
111538
If $S \subseteq X$ is closed, is $f(S,r)$ necessarily closed?
46698
Showing a set is closed under inverses
143457
Is product of two closed sets closed?
49721
Prove the empty set is closed for a metric space (X,d).
18596
A set $A \subset l_1$ is compact if and only if closed, bounded, and one other condition
121135
Why don't we use closed covers to define compactness of metric space?
8015
Compact set plus a closed set is a closed set