Lemma 93.9.5. In Example 93.9.1 assume $X$ is a proper $k$-scheme. Assume $\Lambda $ is a complete local ring with residue field $k$ (the classical case). Then the functor
of isomorphism classes of objects has a hull. If $\text{Der}_ k(\mathcal{O}_ X, \mathcal{O}_ X) = 0$, then $F$ is prorepresentable.
Proof. The existence of a hull follows immediately from Lemmas 93.9.2 and 93.9.4 and Formal Deformation Theory, Lemma 90.16.6 and Remark 90.15.7.
Assume $\text{Der}_ k(\mathcal{O}_ X, \mathcal{O}_ X) = 0$. Then $\mathcal{D}\! \mathit{ef}_ X$ and $F$ are equivalent by Formal Deformation Theory, Lemma 90.19.13. Hence $F$ is a deformation functor (because $\mathcal{D}\! \mathit{ef}_ X$ is a deformation category) with finite tangent space and we can apply Formal Deformation Theory, Theorem 90.18.2. $\square$
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