All Questions
Tagged with abstract-nonsense ag.algebraic-geometry
5 questions
16
votes
2
answers
3k
views
If the direct image of f preserves coherent sheaves on noetherian schemes, how to show f is proper?
The other direction is well known.
I think it is true and I was told by several other guys doing algebraic geometry that it is indeed true but they did not know how to prove. I am also wondering ...
11
votes
1
answer
537
views
Why does this setting imply that a category is Grothendieck?
I came across the following Lemma in Mitsuyasu Hashimoto's Equivariant Twisted Inverses; it is Lemma 11.2 on page 107 of this pdf.
Let $\mathcal{A}$ be an abelian category which satisfies the (AB3) ...
2
votes
0
answers
189
views
Relation between push forward by diagonal morphism and higher direct image functors
Let $f : X \to Y$ be a morphism between two Noetherian schemes. Then $f_*$(respect to $R^1f_*$) sends coherent sheaves to coherent sheaves if and only if $f$ is universally closed (respect to ...
1
vote
1
answer
416
views
Are these two "FUNCTORS" adjoint?
I am considering the following correspondence:
Let $X$ be quasi compact quasi separated schemes.Consider a pseudo functor \begin{equation}Sch\rightarrow CAT :U\mapsto Qcoh(U),f:U\rightarrow V\mapsto f^...
0
votes
0
answers
1k
views
Finite separable extension of fields imply the number of intermediate subfield is finite
The proof of statements either uses Galois theory or Artin primitive element theorem.I would like to know whether there is a proof without using these.The reason to avoid using Galois theory is that ...