Prove the given set is closed
10180
How to prove that this set is closed?
15480
Open set in a metric space is union of closed sets
13906
How to prove the set $S$ is closed under the binary operation $a*b=a+b+kab$?
79424
Don't understand proof that interior of a set is open
78399
In $T_1$ space, all singleton sets are closed?
28683
Sum of two closed sets in $\mathbb R$ is closed?
78300
Showing a set is closed other than giving a counterexample?
153934
How to prove that a set R\Z is open
32441
How to prove or disprove statements about sets
32534
Prove that a set $S \subseteq \mathbb{R}$ is closed and bounded if and only if every sequence in $S$ has a sub sequence converging to a point of $S$.
157603
Continuity $\iff$ Preimage is closed whenever set is closed
102170
Showing a Sequence and its Limit are Closed
106944
Is the set defined by y=sin(1/x) open or closed?
106957
Compact sets are closed?
63717
Is the closure of a set equal to the closure of the closure of that set?
74792
$(X,\tau)$ needs to be $T_1$ in order to guarantee that $A'$ is closed?
99678
Is a sphere a closed set?