If $A$ and $B$ are countable sets, show that $A \times B$ is countable
27937
Cartesian Product of Two Countable Sets is Countable
55978
Prove that for every countable ordinal $\alpha$, $\alpha\times[0,1)$ is order isomoprhic to $[0,1)$
42794
Prove that functions map countable sets to countable sets
132868
Bijection between an infinite set and its union of a countably infinite set
34998
How to prove that $\mathbb{Q}$ ( the rationals) is a countable set
84936
The set of all finite sequences of members of a countable set is also countable
88904
Help with a proof. Countable sets.
136321
Show that if $\sup\big\{\sum\lvert\, f(a)\rvert\big\}  0\}$ is countable.
140440
Proving $(A\times C)\cup(B\times D)\subseteq(A\cup B)\times(C\cup D)$
80916
How to prove that if $A\subseteq A\times A$, then $A=\varnothing$?
157513
How can I prove that these sets are countable infinite?
68139
Show that the set of polynomials with rational coefficients is countable.
23442
Cardinality of the union of infinite and countable sets
44974
Infinite set and countable subsets
147136
Subset of a countable set is itself countable
80759
Proving $A\times (B\cap C)=(A \times B)\cap (A\times C)$.
157081
The cartesian product of a finite amount of countable sets is countable.