Proving $\mathcal{P}(\Bbb N)$ is not countable
52682
Is the power set of the natural numbers countable?
72750
Uncountable number of mutually disjoint countable sets in $\mathbb R$
78412
Representing a countable field by $\Bbb N$ [transport of algebraic structure]
136321
Show that if $\sup\big\{\sum\lvert\, f(a)\rvert\big\}  0\}$ is countable.
110662
Show that $P(\mathbb{N})$ is equivalent to $2^\mathbb{N}$
33157
Proof that an infinite subset of $\mathbb{N}$ is countable
69046
Proof of $\mathbb{Q}$ is not cyclic
21431
The set of all functions from $\mathbb{N} \to \{0, 1\}$ is uncountable?
23907
$Seq (\mathbb{N})$ of all finite sequences of elements of $\mathbb{N}$ is countable.
2269
Proof that the real numbers are countable: Help with why this is wrong
124060
Are these subsets of the powerset P(N) countable?
89749
Example of a not recursively enumerable set $A \subseteq \mathbb{N}$
34998
How to prove that $\mathbb{Q}$ ( the rationals) is a countable set
155168
Is the collection of finite subsets of $\mathbb{Z}$ countable?
136006
Prove that any countable cartesian product of countable sets is countable
130981
Co-countable measure on uncountable set
6491
Not every open set in $\mathbb{R}^n$, for $n\geq2$, is a disjoint union of countable open balls.