Definition 69.6.2. Let S be a scheme. Let f : U \to X be a surjective étale morphism of algebraic spaces over S. Let \mathcal{F} be an object of \textit{Ab}(X_{\acute{e}tale}). The alternating Čech complex1 \check{\mathcal{C}}^\bullet _{alt}(f, \mathcal{F}) associated to \mathcal{F} and f is the complex
\mathop{\mathrm{Hom}}\nolimits (K^0, \mathcal{F}) \to \mathop{\mathrm{Hom}}\nolimits (K^1, \mathcal{F}) \to \mathop{\mathrm{Hom}}\nolimits (K^2, \mathcal{F}) \to \ldots
with Hom groups computed in \textit{Ab}(X_{\acute{e}tale}).
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