Easy proof the set of finite Set in countable is countable
41192
Neatest proof that set of finite subsets is countable?
99656
Prove that the set of all algebraic numbers is countable
103769
The Cartesian product of a finite number of countable sets is countable
138768
Showing that the family of Borel sets is countably generated
145428
Set $A$ is countably infinite if and only if there exists a bijection $f: \mathbb{N} \rightarrow A$
41661
Show that the set of all finite subsets of $\mathbb{N}$ is countable.
120273
Showing that a collection of sets is a $\sigma$-algebra: either set or complement is countable
76240
How is $\epsilon_0$ countable?
127362
How do I prove that there doesn't exist a set whose power set is countable?
81509
The cardinality of a countable union of countable sets, without the axiom of choice
45792
Rigorous proof that surjectivity implies injectivity for finite sets
68430
Proving the countability of algebraic numbers
6523
Prove that the space has a countable dense subset
152563
Set of discontinuity of monotone function is countable
147136
Subset of a countable set is itself countable
44623
Closed set as a countable intersection of open sets
119549
Prove the even integers are countable (by explicitly giving a bijection $\mathbb{N} \to E$)