Is $f(N)$ countable?
94365
How to prove that if $D$ is countable, then $f(D)$ is either finite or countable?
86685
Example of a set $S$ that is countable, but the set of limit points is uncountable
150346
If $f$ is an increasing function defined on $[a,b]$ . Then, $f$ has countable number of discontinuities
14117
Holomorphic function has at most countably zeros
6210
Countable compact spaces as ordinals
146436
Cardinality of the set of bijective functions on $\mathbb{N}$?
34298
sequentially continuous on a non first-countable
48174
Are countable topological spaces second-countable?
78523
Is symmetric group on natural numbers countable?
38711
When can uncountable nouns be countable?
100333
Show A is countable infinity
52429
Explicit countable elementary extension of $\mathbb{N}$
42095
Existence in ZF of a set with countable power set
145428
Set $A$ is countably infinite if and only if there exists a bijection $f: \mathbb{N} \rightarrow A$
63276
Is an arbitrary union of a chain of countable sets countable?
28191
How to show that a set of discontinuous points of an increasing function is at most countable
23907
$Seq (\mathbb{N})$ of all finite sequences of elements of $\mathbb{N}$ is countable.