Prove that the Rationals are Countably Infinite
43268
How to prove that the set of rational numbers are countable?
48804
Enumeration of rationals from Stein-Shakarchi's Real Analysis (Chapter 1, Exercise 24)
156006
Cardinality of set containing all infinite subsets of $\mathbb{Q}$
63804
Proof that every repeating decimal is rational
148516
Proof that $\omega^\omega$ is completely metrizable and second countable
139247
Real Analysis - Prove a set is countable
81943
How to finish proof that $T$ has an infinite model?
94413
Proving Dedekind finite implies finite assuming countable choice
6523
Prove that the space has a countable dense subset
63390
Infinite algebraic extensions of $\mathbb{Q}$
4912
Show that an infinite set $C$ is equipotent to its cartesian product $C\times C$
66301
The cardinality of the set of countably infinite subsets of an infinite set
86988
Cardinality of the Irrationals
119624
A Dedekind infinite set has a countably infinite proper subset
84936
The set of all finite sequences of members of a countable set is also countable
16413
Proving existence of surjective $f:\mathbb{N} \rightarrow A$ implies $A$ is at most countable.
31509
Is axiom of choice necessary for proving that every infinite set has a countably infinite subset?