presheaf which is not a sheaf
6281
example of a gluable unseparated presheaf
68014
Prove that $\mathfrak{su}(2)$ is not isomorphic to $\mathfrak{sl}(2,\mathbb R)$
84707
How to prove a cross is not locally homeomorphic to an euclidean space?
46258
Example of Artinian module that is not Noetherian
143254
Closed ball not a manifold.
19984
Example of topological spaces with continuous bijections that are not homotopy equivalent
76432
$i^{-1} F$ a sheaf if and only if $\varinjlim_{ U \subseteq X \text{ open}, ~ x,y \in U } F(U) \to F_x \times F_y$ is an isomorphism.
90826
Constructing a subset not in $\mathcal{B}(\mathbb{R})$ explicitly
33140
Two non-homeomorphic spaces with continuous bijective functions in both directions
75254
Properties possessed by $H , G/H$ but not G
6646
A (non-artificial) example of a ring without maximal ideals
129929
"sheaves of germs of differentiable functions are by no means coherent"?
158142
Total space of a finite rank locally free sheaf, Vakil's 17.1.4 & 17.1.G
64375
Non-Metrizable Topological Spaces
148434
Ring where irreducibles are primes which is not an UFD
72875
"Naturally occurring" non-Hausdorff spaces?
74330
$\mathbb{R}^n$ not homeomorphic to open subset of $\mathbb{R}^m$