$\aleph_0+\aleph_0=\aleph_0$? or $2\aleph_0$?
12472
Let $X$ and $Y$ be countable sets. Then $X\cup Y$ is countable
29640
If $x \equiv 1 \pmod 3$ and $x \equiv 0 \pmod 2$, what is $x \pmod 6$?
21903
What is the difference between [0-9]+ and [0-9]++?
6427
how many infinite cardinals are smaller than $\aleph$?
73253
Question About equal signs in Theorems
34024
Are +0 and -0 the same?
158257
Is aleph-$0$ a natural number?
141369
If $a+b\equiv0\pmod m$ and $c+d\equiv 0\pmod m$ then $ac\equiv bd\pmod m$. Demonstration.
70266
1-1 correspondence between [0,1] and [0,1)
41731
Question about the order of the product of two elements in an abelian group
110661
When does $\sqrt{a b} = \sqrt{a} \sqrt{b}$?
129813
Is there an easy proof for ${\aleph_\omega} ^ {\aleph_1} = {2}^{\aleph_1}\cdot{\aleph_\omega}^{\aleph_0}$?
105594
Fixed point, union of $\aleph_0, \aleph_{\aleph_0},\aleph_{\aleph_{\aleph_0}}\dots$ [see Noah's comment on notation]
45216
Cardinality of $[0,1]$
124333
A bijection between $\mathbb{N}$ and $\mathbb{P}(\mathbb{N})$?
147564
Why does $(A/I)\otimes_R (B/J)\cong(A\otimes_R B)/(I\otimes_R 1+1\otimes_R J)$?
39878
How to divide aleph numbers