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1 vote
1 answer
216 views

Flatness of "derived local system sheaves"

Let $f: Y\longrightarrow X$ be a smooth proper map of smooth proper schemes over $\mathbb{Q}$, and let $\mathcal{F} = R^1_\text{ét}\overline{f}_*\mathbb{Q}_p$ denote the derived pushforward of $\...
11 votes
2 answers
885 views

intuition about the "section after base-change" for flat descent and exactness of the Amitsur complex

Suppose $A \rightarrow B$ is a faithfully flat map of rings. Then the Amitsur complex is exact: $0 \rightarrow A \rightarrow B \rightarrow B \otimes_A B \rightarrow \dots$ (the second map is $id \...