Lemma 103.15.3. With assumptions and notation as in Lemma 103.15.1 the canonical (base change) map
is an isomorphism for any abelian sheaf \mathcal{F} on \mathcal{X}_{\acute{e}tale} (resp. \mathcal{X}_{fppf}).
Lemma 103.15.3. With assumptions and notation as in Lemma 103.15.1 the canonical (base change) map
is an isomorphism for any abelian sheaf \mathcal{F} on \mathcal{X}_{\acute{e}tale} (resp. \mathcal{X}_{fppf}).
Proof. Comparing the formula for g^{-1}R^ pf_*\mathcal{F} and R^ pf'_*(g')^{-1}\mathcal{F} given in Sheaves on Stacks, Lemma 96.21.2 and Lemma 103.15.2 we see that it suffices to show
where \tau = {\acute{e}tale} (resp. \tau = fppf). Here y is an object of \mathcal{Y} lying over a scheme V such that the morphism y : V \to \mathcal{Y} is smooth (resp. flat). This equality follows from Sheaves on Stacks, Lemma 96.23.3. Although we omit the verification of the assumptions of the lemma, we note that the fact that V \to \mathcal{Y} is smooth (resp. flat) is used to verify the second condition. \square
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