The set of all rational points in the plane is a countable set
27937
Cartesian Product of Two Countable Sets is Countable
14345
If $A\subset\mathbb{R^2}$ is countable, is $\mathbb{R^2}\setminus A$ path connected?
66301
The cardinality of the set of countably infinite subsets of an infinite set
122506
Relation on countable sets
84936
The set of all finite sequences of members of a countable set is also countable
121626
Every open cover of the real numbers has a countable subcover (Lindelöf's lemma)
52682
Is the power set of the natural numbers countable?
99656
Prove that the set of all algebraic numbers is countable
86685
Example of a set $S$ that is countable, but the set of limit points is uncountable
68139
Show that the set of polynomials with rational coefficients is countable.
124060
Are these subsets of the powerset P(N) countable?
155168
Is the collection of finite subsets of $\mathbb{Z}$ countable?
37589
Connectedness of points with both rational or irrational coordinates in the plane?
33157
Proof that an infinite subset of $\mathbb{N}$ is countable
42794
Prove that functions map countable sets to countable sets
138768
Showing that the family of Borel sets is countably generated
102543
Real definition of "countable set"