Proving that $A_1\times A_2 \times \cdots \times A_n$ is countable
136006
Prove that any countable cartesian product of countable sets is countable
149553
Is it always true that $(A_1 \cup A_2) \times (B_1 \cup B_2)=(A_1\times B_1) \cup (A_2 \times B_2)$
80916
How to prove that if $A\subseteq A\times A$, then $A=\varnothing$?
120094
Prove, that for any A, B, C sets, $A\times (B\setminus C) = (A\times B)\setminus (A\times C)$ is true.
4602
Outline of a proof that $\mathbb{R}^2 - A$ where A is countable is path-connected
106606
How to prove that compact subspaces of the Sorgenfrey line are countable?
120642
Let $g : \Bbb N \times \Bbb N \to\Bbb N \times \Bbb N$ defined as $g(m,n) = (m + n,m - n)$
55031
Show any matrix $A_{n\times n}$ can be written as sum of two nonsingular matrices
6523
Prove that the space has a countable dense subset
132778
All distances are rational prove the set is countable
2675
Proof $1+2+3+4+\cdots+n = \frac{n\times(n+1)}2$
135018
Proving that a sequence has $a_n = a_{n+2}$ for $n$ sufficiently large.
144372
How to Prove that if $A$ is bounded, then $A \cdot A$ is bounded?
34998
How to prove that $\mathbb{Q}$ ( the rationals) is a countable set
27937
Cartesian Product of Two Countable Sets is Countable
33157
Proof that an infinite subset of $\mathbb{N}$ is countable
63276
Is an arbitrary union of a chain of countable sets countable?