How can we show that the intersection of a series of closed unbounded sets is closed unbounded?
2044
Club filter of $\kappa$ is $\kappa$-complete
133086
When Cantor's Intersection theorem won't work with closed sets
3896
A closed set in $(A, \mathcal T_A)$ that is not closed in $(X, \mathcal T)$
16654
Unions and Intersections of Open Sets are Open
115625
Intersection of two open dense sets is dense
7607
How to prove that $\mathbb{Q}$ is not the intersection of a countable collection of open sets.
82628
Cardinality of a set of closed intervals
99464
Proof Concerning Indexed family of Sets and Intervals
126897
Showing the set $A+B$ is closed.
78300
Showing a set is closed other than giving a counterexample?
53593
Limits of sequences of sets
55659
Sum of closed and compact set in a TVS
52629
Example 1, Sec. 22 in Munkres' TOPOLOGY, 2nd edition: How to verify that this map is closed?
84609
Unary intersection of the empty set
47680
Prove that the union of the interior of a set and the boundary of the set is the closure of the set
127972
Can distance between two closed sets be zero?
44623
Closed set as a countable intersection of open sets