need one counter example for sum of two closed set need not be closed
28683
Sum of two closed sets in $\mathbb R$ is closed?
12423
"Closed" form for $\sum \frac{1}{n^n}$
86685
Example of a set $S$ that is countable, but the set of limit points is uncountable
70959
Prove that a set $E$ is closed iff it's complement $E^{c}$ is open
127972
Can distance between two closed sets be zero?
126897
Showing the set $A+B$ is closed.
99341
Basic question: closure of irreducible sets
102170
Showing a Sequence and its Limit are Closed
111064
Example of a bounded lattice that is NOT complete
7785
Cardinality of sum-set
158569
Proving a particular subset of $R^n$ is closed
40162
Prove that the set $\mathbb{Q}[\alpha] = \{a+b\alpha+c\alpha^2 \mid a, b, c \in\mathbb{Q}\}$ is closed under addition and multiplication.
5323
Example to show the distance between two closed sets can be 0 even if the two sets are disjoint
123613
Double Complement of a set proof
58101
The set of points where two maps agree is closed?
109462
Looking for a counter example for non-connected intersection of descending chain of closed connected sets
67064
Uncountable minus countable set is uncountable