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Hello,

Is there a proof that the push forward by a proper morphism of Noetherian schemes sends coherent sheaves to coherent ones, without passing in the argument through projective morphisms?

Thank you, Sasha

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Well, you can use Chow's lemma, the result for projective morphisms, and the Leray spectral sequence to get it. Or you can find a different proof here EGA III 3.2.1 here: numdam.org/numdam-bin/feuilleter?id=PMIHES_1961__11_ –  Parsa Dec 6 '11 at 15:38
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@Parsa: If you use Chow's lemma, you are using the result for projective morphisms, which is what Sasha wants to avoid? –  Timo Keller Dec 6 '11 at 17:22
    
If your schemes are locally of finite type over a field k, Antoine Ducros gave a proof that meets your requirements (see arXiv:math/0612521). Basically, the result is known for proper rigid analytic spaces (it is a theorem of Kiehl), so one also gets it for analytifications of proper morphisms (analytifications are to be taken in Berkovich sense, over k endowed with the trivial absolute value) and for proper morphisms themselves. –  Jérôme Poineau Dec 6 '11 at 22:35
    
@Timo: I wasn't sure what he meant by "without passing in the argument through projective morphisms" so I gave an approach assuming proper but not projective (allowing the result for projective) and referenced another proof using only proper. –  Parsa Dec 7 '11 at 0:21
    
Thank you very much for all the references. –  Sasha Dec 18 '11 at 19:26

1 Answer 1

up vote 2 down vote accepted

Gerd Faltings, Finiteness of coherent cohomology for proper fppf stacks, J. Algebraic Geometry 12 (2003) 357–366

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Thank you for the reference. –  Sasha Dec 18 '11 at 19:26

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