The Stacks project

Lemma 34.6.3. Let $T$ be a scheme.

  1. If $T' \to T$ is an isomorphism then $\{ T' \to T\} $ is a syntomic covering of $T$.

  2. If $\{ T_ i \to T\} _{i\in I}$ is a syntomic covering and for each $i$ we have a syntomic covering $\{ T_{ij} \to T_ i\} _{j\in J_ i}$, then $\{ T_{ij} \to T\} _{i \in I, j\in J_ i}$ is a syntomic covering.

  3. If $\{ T_ i \to T\} _{i\in I}$ is a syntomic covering and $T' \to T$ is a morphism of schemes then $\{ T' \times _ T T_ i \to T'\} _{i\in I}$ is a syntomic covering.

Proof. Omitted. $\square$

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