product of quasi-coherent sheaves is not a quasi-coherent sheaf
41180
Arbitrary products of quasi-coherent sheaves?
61926
Why are Grothendieck's and Hartshorne's definitions of quasi-coherence equivalent?
80202
Why is $[0, 1] \cap \mathbb{Q}$ not compact in $\mathbb{Q}$?
72103
Failure of isomorphisms on stalks to arise from an isomorphism of sheaves
71173
Show that $\mathbb{A}^n$ on the Zariski Topology is not Hausdorff, but it is $T_1$
117185
The union of a strictly increasing sequence of $\sigma$-algebras is not a $\sigma$-algebra
107370
An open covering of $\mathbb{Q} \cap [0,1]$ that does not contain any finite subcovering
116350
First axiom of sheaves: in noetherian topological spaces the direct limit presheaf is a sheaf.
43863
Question about left exactness of the section functor for sheaves
80260
Can it happen that the image of a functor is not a category?
86234
Explain why $\mathbb{Z \times Z}$ and $\mathbb{R \times R}$ is not a field
95234
Quasi-components in compact space
20612
Is fibre product of varieties irreducible (integral)?
64130
Prove that $\mathbb{Q}^{\times}$ not isomorphic to $\mathbb{Z}^{n}$
85032
$Q(\mathbb{Z}[t]) / \mathbb{Z}[t]$ is not injective
142101
A direct product of projective modules which is not projective
70577
Product of two Lebesgue integrable functions not Lebesgue integrable