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for questions about etale cohomology of schemes, including foundational material and applications.

6 votes
Accepted

Relationship between topological cohomology and $\ell$-adic cohomology

The way to study the topology of the situation was introduced by Khovanski in "Newton polyhedra, and toroidal varieties" Funkcional. Anal. i Priložen. 11 (1977), no. 4, 56--64, 96. His result (if I ha …
Torsten Ekedahl's user avatar
8 votes
Accepted

Exact sequence in étale cohomology related with proper birational morphism

Let $V := X\setminus E$ and $U := Y\setminus D$ and $j\colon U \rightarrow Y$ and $k\colon V \rightarrow X$ the inclusions. We have exact sequences $\cdots\rightarrow H^\ast(X,k_!\mathbb Z_\ell)\right …
Torsten Ekedahl's user avatar
11 votes
Accepted

Leray-Hirsch principle for étale cohomology

[[ I have added a discussion of when $p$ is smooth or has quotient singularities. ]] [[ I added a discussion on the cohomology of $[X/G]$. ]] The étale case follows in a way that is altogether analog …
Torsten Ekedahl's user avatar
5 votes

If one wants to work with $Q_l$-adic sheaves, should the scheme be of finite type over a 1-d...

At the time of the writing of the 'Adic formalism' the complete finiteness and the formalism of all the relevant operators was only known for the case mentioned (I think that SGA 4 1/2 was the most co …
Torsten Ekedahl's user avatar
2 votes
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For an l-adic sheaf (F_n), why is the complex F_n of finite Tor dimension?

I think you have (slightly) misread your sources. If you take Rapport for instance (which is the one I am familiar with) Deligne never make this claim (as far as I can see). As a typical example consi …
Torsten Ekedahl's user avatar