Separability and second countability
127166
Specific example of a space that is separable but not second countable.
7069
On the product of $\mathfrak c$-many separable spaces
138768
Showing that the family of Borel sets is countably generated
88904
Help with a proof. Countable sets.
27937
Cartesian Product of Two Countable Sets is Countable
74877
Every metric space with a countable base is separable
67050
Every separable metric space has a countable base
12404
Union of definable sets
153651
Countable partition in atoms
23442
Cardinality of the union of infinite and countable sets
18223
Prove that the union of two disjoint countable sets is countable
68430
Proving the countability of algebraic numbers
84936
The set of all finite sequences of members of a countable set is also countable
134844
Summablity and countability
40858
Multiplicative nature of the separability degree
68994
Countable closed sets
97697
Countable union of sets of cardinality $c$ has cardinality $c$