Showing that the set of all algebraic numbers is countable
68430
Proving the countability of algebraic numbers
88904
Help with a proof. Countable sets.
4401
Constructive proof that algebraic numbers form a field
67451
Building a bijection from a finite union of countable sets to $\mathbb{N}$
23442
Cardinality of the union of infinite and countable sets
157081
The cartesian product of a finite amount of countable sets is countable.
128766
Show that the set of functions $\mathbb{N}\to\{0,1\}$ is not countable
130361
Basis for a topology with a countable number of sets
12472
Let $X$ and $Y$ be countable sets. Then $X\cup Y$ is countable
84936
The set of all finite sequences of members of a countable set is also countable
128437
How to prove that a finite set is countable
99478
countably infinite union of countably infinite sets is countable
85895
Proving all rational numbers including negatives are countable
145865
Showing a set is an affine variety
138202
Every open set in $\mathbb{R}$ is a countable union of closed sets
99599
Uncountable and countable
124060
Are these subsets of the powerset P(N) countable?