Situation 38.20.11. Let f : X \to S be a morphism of schemes which is locally of finite type. Let \mathcal{F} be a quasi-coherent \mathcal{O}_ X-module of finite type. For any scheme T over S we will denote \mathcal{F}_ T the base change of \mathcal{F} to T, in other words, \mathcal{F}_ T is the pullback of \mathcal{F} via the projection morphism X_ T = X \times _ S T \to X. Note that X_ T \to T is of finite type and that \mathcal{F}_ T is an \mathcal{O}_{X_ T}-module of finite type (Morphisms, Lemma 29.15.4 and Modules, Lemma 17.9.2). Let n \geq 0. By Definition 38.20.10 and Lemma 38.20.9 we obtain a functor
38.20.11.1
\begin{equation} \label{flat-equation-flat-dimension-n} F_ n : (\mathit{Sch}/S)^{opp} \longrightarrow \textit{Sets}, \quad T \longrightarrow \left\{ \begin{matrix} \{ *\}
& \text{if }\mathcal{F}_ T\text{ is flat over }T\text{ in }\dim \geq n,
\\ \emptyset
& \text{else.}
\end{matrix} \right. \end{equation}
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