What function to use to show that the set of positive rational numbers is countable?
5803
Produce an explicit bijection between rationals and naturals?
86893
Show that it is impossible to list the rational numbers in increasing order
23164
Why are irrational numbers uncountable and rationals countable?
24582
Is the set of sequences of natural numbers with trailing zeros countable?
119549
Prove the even integers are countable (by explicitly giving a bijection $\mathbb{N} \to E$)
28191
How to show that a set of discontinuous points of an increasing function is at most countable
152547
Is the sum of all natural numbers countable?
63276
Is an arbitrary union of a chain of countable sets countable?
41661
Show that the set of all finite subsets of $\mathbb{N}$ is countable.
16722
Proving Gaussian Integers are countable
114442
Completion of rational numbers via Cauchy sequences
34998
How to prove that $\mathbb{Q}$ ( the rationals) is a countable set
83185
How to show countability of $\omega^\omega$ or $\epsilon_0$ in ZF?
9021
An infinite subset of a countable set is countable
136321
Show that if $\sup\big\{\sum\lvert\, f(a)\rvert\big\}  0\}$ is countable.
46967
What is wrong with this proof that the power set of natural numbers is countable?
102543
Real definition of "countable set"