Flawed proof that $P(\mathbb N)$ is countable
124060
Are these subsets of the powerset P(N) countable?
6161
The cartesian product $\mathbb{N} \times \mathbb{N}$ is countable
6491
Not every open set in $\mathbb{R}^n$, for $n\geq2$, is a disjoint union of countable open balls.
32524
Flawed proof that all positive integers are equal
118595
Proving that a set is countable by finding a bijection
62755
The simplest way of proving that $|\mathcal{P}(\mathbb{N})| = |\mathbb{R}| = c$
71922
Prove Uncountable set minus a countable set is uncountable
95747
Number of countable subsets of $\mathbb{R}$
136006
Prove that any countable cartesian product of countable sets is countable
41192
Neatest proof that set of finite subsets is countable?
44974
Infinite set and countable subsets
76240
How is $\epsilon_0$ countable?
120273
Showing that a collection of sets is a $\sigma$-algebra: either set or complement is countable
23442
Cardinality of the union of infinite and countable sets
132778
All distances are rational prove the set is countable
139078
Infinite partition of $\mathbb N$ by infinite subsets
42794
Prove that functions map countable sets to countable sets