Topology open close set
93750
Can a set be neither open nor closed?
80860
How to call a space in which every G$_\kappa$-set is open
157603
Continuity $\iff$ Preimage is closed whenever set is closed
91682
Graph of a continuous function is closed
152193
The intersection of a closure with an open set
68994
Countable closed sets
50344
What is the closure of an open ball $B_X(\mathbf{a},r)$ in $X=\mathbb{R}^n$?
152976
Real Analysis: open and closed sets
42494
The boundary is a closed set
147914
Closed image of locally compact space
35573
A closed ball in a metric space is a closed set
51871
Characterization of Topology
73353
Is it true that a subset that is closed in a closed subspace of a topological space is closed in the whole space?
44430
Is there an open dense set $S \subset [0,1]$ such that $m(S)<1$?
99678
Is a sphere a closed set?
148213
Given a topological space $X$, why are both $X$ and $\emptyset$ open and closed?
108864
Showing that two topologies give rise to the same topology