Definition 59.96.1. Let f : X \to Y be a quasi-compact and quasi-separated morphism of schemes. The cohomological dimension of f is the smallest element
\text{cd}(f) \in \{ 0, 1, 2, \ldots \} \cup \{ \infty \}
such that for any abelian torsion sheaf \mathcal{F} on X_{\acute{e}tale} we have R^ if_*\mathcal{F} = 0 for i > \text{cd}(f).
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