A doubt about real analysis concerning countable sets
102543
Real definition of "countable set"
33157
Proof that an infinite subset of $\mathbb{N}$ is countable
41661
Show that the set of all finite subsets of $\mathbb{N}$ is countable.
83842
Alternate proofs (other than diagonalization and topological nested sets) for uncountability of the reals?
68230
The cardinality of a countable union of sets with less than continuum cardinality
147136
Subset of a countable set is itself countable
128118
Is the cofinite topology on a countable set first countable?
7607
How to prove that $\mathbb{Q}$ is not the intersection of a countable collection of open sets.
98151
Suppose that A is a countable set. Show that the set B is also countable if there is an onto function f from A to B.
1396
cardinality of all real sequences
66398
Union of a finite set and a countably infinite set is countably infinite
20706
Non-existence of a Surjective Function from a Set to Its Subsets (Cantor's theorem)
86685
Example of a set $S$ that is countable, but the set of limit points is uncountable
44974
Infinite set and countable subsets
80096
Prove that the union of countably many countable sets is countable.
37398
Proof that$ (a+A)\cap A=\varnothing$ if $A$ is countable
88904
Help with a proof. Countable sets.