Standard $n$-simplex is not a Kan complex
116783
Simplicial sets which are not Kan complexes
10724
Case of the 'mice problem' for $n=3$
118007
Not lifting your pen on the $n\times n$ grid
104509
The center of $A_n$ is trivial for $n \geq 4$
110054
An easy question on complex
49242
stab(S) is isomorphic to $ S_k \times S_{n-k} $
130073
$N(ab) \geq N(a)$ is not necessary for the ring to be euclidean
53331
$\mathbb{Q}(\sqrt2, \sqrt3)$ is not isomorphic to $\mathbb{Q}(\sqrt[4]2)$
58508
Number of ways to pair off $2n$ points such that no chords intersect
156457
Show that $K[x,xy,xy^2,\dots]$ is not Noetherian
142861
Multipartite graphs which are not planar
64130
Prove that $\mathbb{Q}^{\times}$ not isomorphic to $\mathbb{Z}^{n}$
70576
Elementary proof that $\mathbb{R}^n$ is not homeomorphic to $\mathbb{R}^m$
74330
$\mathbb{R}^n$ not homeomorphic to open subset of $\mathbb{R}^m$
26449
$|G|=24$ prove that $G$ is not simple
8066
Sort-of-simple non-Hopfian groups
20296
The ideal $I= \langle x,y \rangle\subset k[x,y]$ is not principal