Lemma 30.2.2. Let $X$ be a scheme. Let $\mathcal{F}$ be a quasi-coherent $\mathcal{O}_ X$-module. For any affine open $U \subset X$ we have $H^ p(U, \mathcal{F}) = 0$ for all $p > 0$.
Serre vanishing: Higher cohomology vanishes on affine schemes for quasi-coherent modules.
Proof.
We are going to apply Cohomology, Lemma 20.11.9. As our basis $\mathcal{B}$ for the topology of $X$ we are going to use the affine opens of $X$. As our set $\text{Cov}$ of open coverings we are going to use the standard open coverings of affine opens of $X$. Next we check that conditions (1), (2) and (3) of Cohomology, Lemma 20.11.9 hold. Note that the intersection of standard opens in an affine is another standard open. Hence property (1) holds. The coverings form a cofinal system of open coverings of any element of $\mathcal{B}$, see Schemes, Lemma 26.5.1. Hence (2) holds. Finally, condition (3) of the lemma follows from Lemma 30.2.1.
$\square$
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Comment #3020 by Brian Lawrence on