Situation 27.3.1. Here $S$ is a scheme, and $\mathcal{A}$ is a quasi-coherent $\mathcal{O}_ S$-algebra. This means that $\mathcal{A}$ is a sheaf of $\mathcal{O}_ S$-algebras which is quasi-coherent as an $\mathcal{O}_ S$-module.

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