Countable set of number rational, prove with $\mathbb{Z}$.
34998
How to prove that $\mathbb{Q}$ ( the rationals) is a countable set
16413
Proving existence of surjective $f:\mathbb{N} \rightarrow A$ implies $A$ is at most countable.
103717
Topological Property of the Set of Integers
4381
Proof that the set of irrational numbers is dense in reals
2269
Proof that the real numbers are countable: Help with why this is wrong
32848
Prove that the product of a non-zero rational and irrational number is irrational.
154474
Image of countable and uncountable sets
30478
How to prove that a number is irrational
23164
Why are irrational numbers uncountable and rationals countable?
132778
All distances are rational prove the set is countable
4518
How would one go about proving that the rationals are not the countable intersection of open sets?
121831
Proving that rational numbers are dense
156006
Cardinality of set containing all infinite subsets of $\mathbb{Q}$
96647
Number theory: Problem involving rational numbers
68139
Show that the set of polynomials with rational coefficients is countable.
13550
For an irrational number $\alpha$, prove that the set $\{a+b\alpha: a,b\in \mathbb{Z}\}$ is dense in $\mathbb R$
35692
The set of all finite subsets of the natural numbers is countable