Countability of sets with countable coefficients
129109
Is the set of polynomial with coefficients on $\mathbb{Q}$ enumerable?
6523
Prove that the space has a countable dense subset
68430
Proving the countability of algebraic numbers
66398
Union of a finite set and a countably infinite set is countably infinite
91237
Every infinite set contains a countable subset
80019
$\varepsilon$-number countability without choice
81509
The cardinality of a countable union of countable sets, without the axiom of choice
70143
Mutually exclusive countable subsets of a countable set
67064
Uncountable minus countable set is uncountable
130361
Basis for a topology with a countable number of sets
75019
Infinite Cartesian product of countable sets is uncountable
130981
Co-countable measure on uncountable set
66301
The cardinality of the set of countably infinite subsets of an infinite set
80096
Prove that the union of countably many countable sets is countable.
102543
Real definition of "countable set"
68994
Countable closed sets
67451
Building a bijection from a finite union of countable sets to $\mathbb{N}$