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Singularities in algebraic/complex/differential geometry and analysis of ODEs/PDEs. Singular spaces, vector fields, etc.

5 votes
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Factoriality vs $\mathbf{Q}$-factoriality for threefolds hypersurfaces with isolated singula...

The answer to Question 2 is true. If $(R,m)$ is a local complete intersection of equicharacterstic $0$ and of dimension $3$ then the Picard group of $Y = \text{Spec} R-\{m\}$ is torsion-free. This gr …
Hailong Dao's user avatar
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6 votes

What formal properties should resolution of singularities have?

It should exist in all characteristics, even mixed characteristic! This sounds somewhat cheeky, but I was fairly serious. To algebraists, and the OP is one last time I met him, a purely ring-the …
Hailong Dao's user avatar
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5 votes

Q-factorial and rational singularities on surfaces

About the converse: one does need all the assumptions Karl mentioned in his answer. There are $2$-dim. complete local rings which are UFD but does not have rational singularity. One such example (due …
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4 votes
Accepted

Relationship between Hilbert-Samuel multiplicity and polar multiplicity

First, the quantity you defined is the Hilbert-Samuel multiplicity of the ideal $J= (f_x,f_y)$ in $R=\mathbb C[[x,y]]/(f)$. The multiplicity of $f$ usually refers to the multiplicity of the maximal id …
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0 votes

on the relative conductor of curve singularity and quotient of ideals

Ok, so it has been 7 years, but I do have something new to add to the answers by Karl and Sándor. All your questions are about whether some modules/ideals are reflexive. That is because for a fraction …
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1 vote

Tame ramification of (mild) curve singularities.

Here is a reference that may be relevant (you may know it already): Auslander-Rim has a paper called "Ramification index and multiplicity" . Even though they mostly discussed normal rings, their defin …
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5 votes
Accepted

Computations of divisor class monoids

Here are a few remarks about $DC(A)$ (assuming $A$ is a complete Noetherian local domain of dimension $1$). The equivalence relation in $D(A)$ is just isomorphism as $A$-modules. So you can view $DC( …
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