how to prove finite subset of a countable set is countable
41192
Neatest proof that set of finite subsets is countable?
12472
Let $X$ and $Y$ be countable sets. Then $X\cup Y$ is countable
51094
Prove that the set of integer coefficients polynomials is countable
76240
How is $\epsilon_0$ countable?
124060
Are these subsets of the powerset P(N) countable?
99478
countably infinite union of countably infinite sets is countable
68994
Countable closed sets
134071
If A is a finite set and B is an infinite set, then B\A is an infinite set
80096
Prove that the union of countably many countable sets is countable.
154474
Image of countable and uncountable sets
33157
Proof that an infinite subset of $\mathbb{N}$ is countable
34998
How to prove that $\mathbb{Q}$ ( the rationals) is a countable set
18223
Prove that the union of two disjoint countable sets is countable
103769
The Cartesian product of a finite number of countable sets is countable
48523
Let $A$ be any uncountable set, and let $B$ be a countable subset of $A$. Prove that the cardinality of $A = A - B $
120562
If A is an infinite set and B is at most countable set, prove that A and $A \cup B$ have the same cardinality
99656
Prove that the set of all algebraic numbers is countable