Basis for co-countable topology
140168
What are the basis for co-countable and co-finite topologies
40937
Is the set of partial order relations over $ \mathbb{N}$ countable?
81423
Completeness and Topological Equivalence
88028
Topology - closures of intervals with the order topology
95747
Number of countable subsets of $\mathbb{R}$
52429
Explicit countable elementary extension of $\mathbb{N}$
67050
Every separable metric space has a countable base
133266
If $(X, \mathcal{T})$ has a countable subbasis, then it has a countable basis
136094
$G_\delta$ singletons in compact Hausdorff and first countability
74877
Every metric space with a countable base is separable
99353
Topology on cartesian product and product topology.
138768
Showing that the family of Borel sets is countably generated
112050
Union of ascending chain of Topologies
59289
Nested Sequence of Topological Space and the Coherent Topology; Munkres Topology 35.9
23442
Cardinality of the union of infinite and countable sets
16649
Topological space with countable open cover $\{U_\alpha\} $ with each $U_\alpha$ second-countable, is second countable
47251
Non-compactness of $\mathbb{R}$ with the cocountable topology