Proving a set to be a topology
120685
Topology induced from Kuratowski Closure properties
77563
Homeomorphism between spaces equipped with cofinite topologies
79424
Don't understand proof that interior of a set is open
106298
Prove that some topology is not metrizable
82825
Proving set of interiors is open
17461
Show that a set is dense in $[-1,1]$
28637
Proving continuous image of compact sets are compact
59424
Showing that $B=\{(x,y) \in \Bbb{R^2} \mid \ xy>0 \}$ is an open set
157578
perfect map in topology
134999
Writing empty set as union of basis elements for a topology.
19856
Prove that a subset of a separable set is itself separable
33310
Proving that the set of limit points of a set is closed
104308
Proving a set is a Sigma Algebra
103717
Topological Property of the Set of Integers
144383
The closure of a connected set in a topological space is connected
9268
Proving that the Union of Two Compact Sets is Compact
10180
How to prove that this set is closed?