Lemma 31.8.3. Let f : X \to S be a morphism of schemes. Let i : Z \to X be a finite morphism. Let \mathcal{F} be a quasi-coherent \mathcal{O}_ Z-module. Then \text{WeakAss}_{X/S}(i_*\mathcal{F}) = i(\text{WeakAss}_{Z/S}(\mathcal{F})).
Proof. Let i_ s : Z_ s \to X_ s be the induced morphism between fibres. Then (i_*\mathcal{F})_ s = i_{s, *}(\mathcal{F}_ s) by Cohomology of Schemes, Lemma 30.5.1 and the fact that i is affine. Hence we may apply Lemma 31.6.3 to conclude. \square
Comments (0)
There are also: