Counter example of monotone union
10602
Monotone Union of subgroups being subgroup
39382
Examples of the Pigeonhole Principle
93952
Show that $X$ can be represented as a union of disjoint equivalence classes
55661
Existence of two disjoint closed sets with zero infimal distance
112491
Finding counterexamples for infinite series.
130156
Image of the union and intersection of sets.
18223
Prove that the union of two disjoint countable sets is countable
94203
Examples for almost-semirings without absorbing zero
152563
Set of discontinuity of monotone function is countable
111064
Example of a bounded lattice that is NOT complete
70143
Mutually exclusive countable subsets of a countable set
89749
Example of a not recursively enumerable set $A \subseteq \mathbb{N}$
20140
Example of set which contains itself
149390
Fixed point of a Function (monotonically increasing)
129227
An example of neither open nor closed set
76597
Examples of provably${}^n$ unprovable statements
23442
Cardinality of the union of infinite and countable sets