Is a well-ordered subset of $(\mathbb{R},<)$ countable?
70196
Is there any well-ordered uncountable set of real numbers under the original ordering?
48174
Are countable topological spaces second-countable?
60678
Does 'A countable infinite Cartesian product of countable sets is not necessarily countable' violate induction principle?
147136
Subset of a countable set is itself countable
81509
The cardinality of a countable union of countable sets, without the axiom of choice
9021
An infinite subset of a countable set is countable
134844
Summablity and countability
127233
Cardinality of order types in $\mathbb{N}$
33157
Proof that an infinite subset of $\mathbb{N}$ is countable
124060
Are these subsets of the powerset P(N) countable?
45878
Elementary Set Theory: Ordinals, Well Orderings and Isomorphisms
63276
Is an arbitrary union of a chain of countable sets countable?
139247
Real Analysis - Prove a set is countable
119624
A Dedekind infinite set has a countably infinite proper subset
122506
Relation on countable sets
43024
Well-ordered sets, properties of an element that is not largest in the set
136006
Prove that any countable cartesian product of countable sets is countable