How to prove that every infinite subset of a denumerable set is denumerable?
9021
An infinite subset of a countable set is countable
72190
Topological proof on discrete topology where $X$ is infinite
19856
Prove that a subset of a separable set is itself separable
88904
Help with a proof. Countable sets.
155168
Is the collection of finite subsets of $\mathbb{Z}$ countable?
91163
Let the set S be infinite, and the set T countably infinite. Show that S and S U T have the same cardinality
122947
What is the cardinality of the set of infinite cardinalities?
38507
Show that $\mathbb{Q}\times \mathbb{Q}$ is denumerable
108922
Cardinality and infinite sets: naturals, integers, rationals, bijections
89749
Example of a not recursively enumerable set $A \subseteq \mathbb{N}$
56233
Is the set of all strings with countably infinite length bijective to $[0,1]$?
109070
Question about the proof of the distributive property for sets
12404
Union of definable sets
48523
Let $A$ be any uncountable set, and let $B$ be a countable subset of $A$. Prove that the cardinality of $A = A - B $
128437
How to prove that a finite set is countable
70143
Mutually exclusive countable subsets of a countable set
33157
Proof that an infinite subset of $\mathbb{N}$ is countable