Is the Sorgenfrey Line second countable?
62793
$\mathbb{R}$ with the lower limit topology is not second-countable
52110
About the second fundamental form
2269
Proof that the real numbers are countable: Help with why this is wrong
28539
Does any uncountable set contain two disjoint uncountable sets?
32774
Finite Cartesian Product of Countable sets is countable?
34833
COUNT(*) vs. COUNT(1) vs. COUNT(pk): which is better?
30022
Why use the double cover instead of the universal cover of $SO(2)$?
5584
How strong is this second-order version of ZFC?
16649
Topological space with countable open cover $\{U_\alpha\} $ with each $U_\alpha$ second-countable, is second countable
91490
“Firstly, secondly” vs. “Firstly, lastly” when listing just two points
68430
Proving the countability of algebraic numbers
118595
Proving that a set is countable by finding a bijection
42336
The Line with two origins
55717
cardinality of the Borel $\sigma$-algebra of a second countable space
100333
Show A is countable infinity
40566
Counting surjective functions
95747
Number of countable subsets of $\mathbb{R}$