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

6 votes
3 answers
713 views

Ascending chain condition on radical ideals

There is a basic theorem in the geometry of schemes saying that the Spec of a Noetherian ring is a Noetherian topological space. It can be formulated as the ACC condition implies the ACCR condition (t …
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11 votes

A geometric proof of Krull's Principal ideal theorem

Anon's answer gives a beautiful geometric proof when $A$ is a variety. Below I am trying to give some geometric interpretation of the usual algebraic proof. First a disclaimer: I'm not an algebraist, …
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  • 5,169
6 votes
1 answer
837 views

UFD and fundamental group

Let $C$ be the curve $x^2+y^2-1$, defined over $\mathbb R$. It is easy to see that $\mathbb R[C]$ is not a UFD, as witnessed by the identity $(1-x)(1+x)=y^2$. On the other hand, the real locus $C(\mat …
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  • 5,169
3 votes
1 answer
2k views

Completion of a finite field extension is also finite?

Let $(L,w)/(K,v)$ be a finite extension of valuation fields, and let $L_w$, $K_v$ be the respective completions of $(L,w)$, $(K,v)$. Is the field extension $L_w/K_v$ finite? For nonarchimedean valuat …
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5 votes

Localization and containment in commutative ring

The conclusion is true if and only if $R$ has at most 1 maximal ideal, i.e., $R$ is either itself a local ring, or the zero ring. The "if" part is trivial: for the case of local ring see the comment a …
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