Open and Closed Sets in the Euclidean Space R^n
95244
Prove that a finite union of closed sets is also closed
152976
Real Analysis: open and closed sets
36237
Closed set mapped to itself in a compact Hausdorff space
114608
Proof concerning regular space: there exist a closed set contained in any open set containing $x$
73130
A simple question about open set
38581
Construct a Borel set on R such that it intersect every open interval with non-zero non-"full" measure
40438
Proving that closed (and open) balls are convex
70264
Prove that the inverse image of an open set is open
158569
Proving a particular subset of $R^n$ is closed
135814
Prove certain subsets of $\mathbb R^n$ are subspaces
74330
$\mathbb{R}^n$ not homeomorphic to open subset of $\mathbb{R}^m$
110957
No non-trivial clopen sets in $\mathbb{R}$? How to give a direct proof?
115272
Showing that projections $\mathbb{R}^2 \to \mathbb{R}$ are not closed
18334
Equivalence between CH and existence of certain sets in $\mathbb{R}^2$
67259
Can we prove that a bounded closed subset of $\mathbb R^n$ is compact without Axiom of Choice?
157753
Show that any set in a metric space can be written as the intersection of open sets
105445
Are the rationals a closed or open set in $\mathbb{R}$?