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Commutative rings, modules, ideals, homological algebra, computational aspects, invariant theory, connections to algebraic geometry and combinatorics.

4 votes
1 answer
250 views

Can relative flatness of a sheaf be tested using (faithfully) flat morphisms?

Given a $\mathbb{C}$-scheme $S$, two $S$-schemes $X$ and $Y$ that are flat over $S$ and a coherent sheaf of $O_Y$-modules $F$. Assume we have a (faithfully) flat $S$-morphism $\pi: X \rightarrow Y$ a …
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3 votes
0 answers
327 views

Which sheaves on a projective bundle are flat over the base scheme?

Assume $X$ is a noetherian scheme over $\mathbb{C}$ and $E$ a locally free sheaf of finite rank on $X$. Denote the the associated projective bundle by $f: \mathbb{P}(E)\rightarrow X$. Are there any c …
Bernie's user avatar
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0 votes
1 answer
109 views

How to find ideals of finite length in a power series ring with special properties?

Let $A$ be the power series ring $\mathbb{C}[[x,y]]$. Assume we are given two ideals $I,J$ of finite length in $A$ such that: $xJ\subseteq I\subseteq J$ Is it possible to find ideals of finite le …
Bernie's user avatar
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0 votes
0 answers
80 views

A quaternion x generates a left ideal of rank 2 if and only if x, ix and jx are linearly dep...

I am trying to understand the construction of Artin and Mumford of a non-rational unirational threefold in ([1], p.90). Assume $S$ is a smooth projective surface over $\mathbb{C}$ with a smooth curv …
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