Showing countability without explicit bijection
5803
Produce an explicit bijection between rationals and naturals?
23464
How to find a explicit bijection for some $f:A\times B \rightarrow B \times A$
91938
Countable Matrix Representation
111954
Computing the cardinality of a combinatorial set
113109
Showing that a map is bijective and finding its inverse
130981
Co-countable measure on uncountable set
24685
Expressing a Countable Union of Sets as the Countable Union of Disjoint Sets (e.g. Eliminating Duplicate Intersections)
120522
Showing any countable, dense, linear ordering is isomorphic to a subset of $\mathbb{Q}$
23442
Cardinality of the union of infinite and countable sets
18429
Counting measure proof
100134
Proving existence of a surjection $2^{\aleph_0} \to \aleph_1$ without AC
155777
Show that infinite Cartesian product is uncountable
90566
There exists surjections from A onto B and vice versa, and there is no bijection between the sets?
124847
Is the set of surjective functions from $\mathbb{N}$ to $\mathbb{N}$ uncountable?
40566
Counting surjective functions
70143
Mutually exclusive countable subsets of a countable set
78225
Countable additivity implies countable subadditivity?