Open and Closed sets of $\Omega$
107160
Open Set and Measure Theory
143457
Is product of two closed sets closed?
28500
What are the components and path components of $\mathbb{R}^{\omega}$ in the product, uniform, and box topologies?
144383
The closure of a connected set in a topological space is connected
9320
Extension of continuous function on a closed subset of $\mathbb{R}$
102048
Closure of a compact set in Regular space $ X $
135454
An open interval is an open set?
11405
If a nonempty set of real numbers is open and closed, is it $\mathbb{R}$? Why/Why not?
60004
Why is $\omega$ the smallest $\infty$?
30079
Is for open connected $U$ the set $U_\varepsilon$ for small $\varepsilon$ connected?
49220
Open Sets of $\mathbb{R}^1$ and axiom of choice
66301
The cardinality of the set of countably infinite subsets of an infinite set
92639
Prove that the family of open sets in $\mathbb{R}$ has cardinality equal to $2^{\aleph_0}$
137460
How should I think of an open vs. closed set?
127173
Closed subset of compact set is compact
42494
The boundary is a closed set
78117
Closed property of nonempty finite set