Why isn't a loop on $S^1$ nullhomotopic?
5540
Why aren't these loops homotopic?
23837
Why is $\mathbb{R}/{\sim}$ not first countable at $[0]$, where $x \sim y \Leftrightarrow x = y\text{ or }x,y \in \mathbb{Z}$?
44069
Proof that a continuous map to $S^n$ whose image is a proper subset of $S^n$ is null-homotopic
97040
Question about an application of the Rank-Nullity theorem
63516
$C^1[0,1]$ is not complete with respect to sup norm
62941
1/z on an annulus has no anti-derivative
118903
The sup norm on $C[0,1]$ is not equivalent to another one, induced by some inner product
15435
how to check if $1 and $2 are null?
57070
Dimensionality of null space when Trace is Zero
110202
Is the image of a null set under a differentiable map always null?
55864
Is there a null sequence that is in not in $\ell_p$ for any $p<\infty$?
17525
Why the interior of $\mathbb{Q}$ in $\mathbb{R}$ is empty?
96584
Why isn't the volume formula for a cone $\pi r^2h$?
93923
No surjective bounded linear map from $\ell^2(\mathbf{N})$ to $\ell^1(\mathbf{N})$
59804
Show that the plane $\{su+tv|s,t \in\Bbb R\}$ in $\Bbb R^3$ is equal to the null space of some element of $(\Bbb R^3)^{*}$.
23580
Range of A and null space of the transpose of A
88813
SphericalHarmonicY does not seem to be an eigenfunction of the spherical harmonic equation