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The Stacks project

Remark 90.6.4. Let p : \mathcal{F} \to \mathcal{C}_\Lambda be a category cofibered in groupoids, and let x \in \mathop{\mathrm{Ob}}\nolimits (\mathcal{F}(k)). We denote by \mathcal{F}_ x the category of objects over x. An object of \mathcal{F}_ x is an arrow y \to x. A morphism (y \to x) \to (z \to x) in \mathcal{F}_ x is a commutative diagram

\xymatrix{ y \ar[rr] \ar[dr] & & z \ar[dl] \\ & x & }

There is a forgetful functor \mathcal{F}_ x \to \mathcal{F}. We define the functor p_ x : \mathcal{F}_ x \to \mathcal{C}_\Lambda as the composition \mathcal{F}_ x \to \mathcal{F} \xrightarrow {p} \mathcal{C}_\Lambda . Then p_ x : \mathcal{F}_ x \to \mathcal{C}_\Lambda is a predeformation category (proof omitted). In this way we can pass from an arbitrary category cofibered in groupoids over \mathcal{C}_\Lambda to a predeformation category at any x \in \mathop{\mathrm{Ob}}\nolimits (\mathcal{F}(k)).


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