The Stacks project

Definition 35.22.1. Let $\mathcal{P}$ be a property of morphisms of schemes over a base. Let $\tau \in \{ fpqc, fppf, syntomic, smooth, {\acute{e}tale}, Zariski\} $. We say $\mathcal{P}$ is $\tau $ local on the base, or $\tau $ local on the target, or local on the base for the $\tau $-topology if for any $\tau $-covering $\{ Y_ i \to Y\} _{i \in I}$ (see Topologies, Section 34.2) and any morphism of schemes $f : X \to Y$ over $S$ we have

\[ f \text{ has }\mathcal{P} \Leftrightarrow \text{each }Y_ i \times _ Y X \to Y_ i\text{ has }\mathcal{P}. \]

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