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Algebraic varieties, stacks, sheaves, schemes, moduli spaces, complex geometry, quantum cohomology.

0 votes

are deformations of torsion modules always torsion?

[I'm going to work over k[h] as the base instead; I don't think anything changes, but if I'm wrong you should let me know.] Consider the case M = k[s,t,h]/(st-h^2). Setting h=0 yields M_0 = k[s,t]/( …
Charley's user avatar
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5 votes
Accepted

If $\Omega_{X/Y}$ is locally free of rank $\mathrm{dim}\left(X\right)-\mathrm{dim}\left(Y\ri...

I think Ishai's example is close, but one must be a little careful; the normalization of the node is a good example, but the normalization of the cusp is ramified, and the sheaf of relative differenti …
Charley's user avatar
  • 916
11 votes

What is the universal property of normalization?

Normalization is right adjoint to the inclusion functor from the category of normal schemes into the category of reduced schemes. In other words, if $n:Y\rightarrow X$ is the normalization of $X$ and …
Charley's user avatar
  • 916
20 votes
Accepted

What is the universal property of normalization?

I've realized that my answer is wrong. Here's the right answer: if $Z$ is a normal scheme and $f: Z \to X$ is a morphism such that each associated point of $Z$ maps to an associated point of $X$, the …
Charley's user avatar
  • 916