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When you say "deformation functor", you have to be careful to specify exactly which functor you are thinking about. There are two relevant deformation functors at play here.

One is the functor $D$ of abstract deformations of $Y$. If $A$ is an Artin local $k$-algebra, then $D(A)$ is the set of isomorphism classes of flat families $Y_A$ over $A$ whose central fiber is isomorphic to $Y$.

The other functor $D'$ is the functor of deformations of $Y$ inside $\mathbb{P}^n_k$; here\mathbb{P}^n_k$. Here,$D'(A)$is the set of isomorphism classes of flat families$Y_A$together with an embedding$Y_A \rightarrow \mathbb{P}^n_k \times Spec A$such that the central fiber is$Y \rightarrow \mathbb{P}^n_k$(not isomorphic to$Y$, but exactly$Y$, as we are talking about subschemes of$\mathbb{P}^n_k$). The functor$D$does not have any direct relationship to the Hilbert scheme, but the functor D' certainly does. Given any scheme$X$and a point$x \in X$, the local ring$\mathcal{O}_x$defines a functor$F: (Art)_k \rightarrow (Sets)$by setting$F(A) = Hom(Spec A, Spec \mathcal{O}_x)$. We say that$F$is pro-represented by$\mathcal{O}_x$. If you take the local ring$\mathcal{O}_{[Y]}$of the Hilbert scheme (which you probably know to be representable by an honest scheme by a theorem of Grothendieck) at the point$[Y]$, then the functor it pro-represents is none other than$D'$. Being pro-representable is stronger than having a versal deformation space; it means that the functor has a universal deformation space, which is the formal completion of the point whose local ring is doing the pro-representing. So the (uni)versal deformation space of$D'$is the formal completion of the point$[Y]$in the Hilbert scheme. As for the versal deformation space of$D$, I am not really sure what it looks like, but there is a morphism$D' \rightarrow D$of deformation functors given by forgetting the embedding of$Y_A \rightarrow \mathbb{P}^n_k \times Spec A$. In general, I think of a versal deformation space as an infinitesimal object; it is only keeping track of what happens when you deform$Y$a little bit. The Hilbert scheme, on the other hand, is global; it is keeping track of all subschemes with the same Hilbert polynomial as$Y$, including ones which might be far away from$Y$(if$Y$was a point, for instance). Thus, you would expect the versal deformation space of the appropriate functor to map into the Hilbert scheme, rather than the other way around. 3 added 178 characters in body; added 239 characters in body When you say "deformation functor", you have to be careful to specify exactly which functor you are thinking about. There are two relevant deformation functors at play here. One is the functor$D$of abstract deformations of$Y$. If$A$is an Artin local$k$-algebra, then$D(A)$is the set of isomorphism classes of flat families$Y_A$over$A$whose central fiber is isomorphic to$Y$. The other functor$D'$is the functor of deformations of$Y$inside$\mathbb{P}^n_k$; here,$D'(A)$is the set of isomorphism classes of flat families$Y_A$together with an embedding$Y_A \rightarrow \mathbb{P}^n_k \times Spec A$such that the central fiber is$Y \rightarrow \mathbb{P}^n_k$(not isomorphic to$Y$, but exactly$Y$, as we are talking about subschemes of$\mathbb{P}^n_k$). The functor$D$does not have any direct relationship to the Hilbert scheme, but the functor D' certainly does. Given any scheme$X$and a point$x \in X$, the local ring$\mathcal{O}_x$defines a functor$F: (Art)_k \rightarrow (Sets)$by setting$F(A) = Hom(Spec A, Spec \mathcal{O}_x)$. We say that$F$is pro-represented by$\mathcal{O}_x$. If you take the local ring$\mathcal{O}_{[Y]}$of the Hilbert scheme (which you probably know to be representable by an honest scheme by a theorem of Grothendieck) at the point$[Y]$, then the functor it pro-represents is none other than$D'$. As Being pro-representable is stronger than having a side remarkversal deformation space; it means that the functor has a universal deformation space, which is the formal completion of the point whose local ring is doing the pro-representing. So the (uni)versal deformation space of$D'$is the formal completion of the point$[Y]$in the Hilbert scheme. As for the versal deformation space of$D$, I am not really sure what it looks like, but there is a morphism$D' \rightarrow D$of deformation functors given by forgetting the embedding of$Y_A \rightarrow \mathbb{P}^n_k \times Spec A$. 2 added 21 characters in body; added 4 characters in body; added 51 characters in body When you say "deformation functor", you have to be careful to specify exactly which functor you are thinking about. There are two relevant deformation functors at play here. One is the functor$D$of abstract deformations of$Y$. If$A$is an Artin local$k$-algebra, then$D(A)$is the set of isomorphism classes of flat families$Y_A$over$A$whose central fiber is isomorphic to$Y$. The other functor$D'$is the functor of deformations of$Y$inside$P^n_k$; \mathbb{P}^n_k$; here, $D'(A)$ is the set of isomorphism classes of flat families $Y_A$ together with an embedding $Y_A \rightarrow \bb{P}^n_k mathbb{P}^n_k \times Spec A$ such that the central fiber is $Y \rightarrow \bb{P}^n_k$ mathbb{P}^n_k$(not isomorphic to$Y$, but exactly$Y$, as we are talking about subschemes of$\bb{P}^n_k$).\mathbb{P}^n_k$).

The functor $D$ does not have any direct relationship to the Hilbert scheme, but the functor D' certainly does.

Given any scheme $X$ and a point $x \in X$, the local ring $O_x$ \mathcal{O}_x$defines a functor$F: (Art)_k \rightarrow (Sets)$by setting$F(A) = Hom(O_x,A)$. Hom(Spec A, Spec \mathcal{O}_x)$. We say that $F$ is pro-represented by $O_x$.\mathcal{O}_x$. If you take the local ring$O_{[Y]}$\mathcal{O}_{[Y]}$ of the Hilbert scheme (which you probably know to be representable by an honest scheme by a theorem of Grothendieck) at the point $[Y]$, then the functor it pro-represents is none other than $D'$.

As a side remark, there is a morphism $D' \rightarrow D$ of deformation functors given by forgetting the embedding of $Y_A \rightarrow \bb{P}^n_k mathbb{P}^n_k \times Spec A$.

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