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Non-commutative rings and algebras, non-associative algebras. Can be used in combination with ra.rings-and-algebras

22 votes
Accepted

Are there any finitely generated artinian modules that are not Noetherian?

Suppose you have an Artinian but not Noetherian finitely generated $R$ module $M$. Let $0\leq M_1\leq M_2\leq \cdots \leq M_n=M$ be a finite chain of $R$-modules such that each composition factor $M_i …
Simon Wadsley's user avatar
10 votes

Why should the tensor product of $\mathcal{D}_X$-modules over $\mathcal{O}_X$ be a $\mathcal...

One way to think about this is that $D$ is the universal enveloping algebra $U(R,L)$ of the $(k,R)$ Lie-Rinehart algebra $\mathrm{Der}_k(R,R)$. Whenever one has such an enveloping algebra one may perf …
Simon Wadsley's user avatar
7 votes

Faithful flatness and non-commutative algebras

If $A$ happens to be (left) Noetherian then to show $f$ makes $B$ a faithfully flat right $A$-module it is enough to check that $B\otimes_A S\neq 0$ for every simple (left) $A$-module $S$ since, in th …
Simon Wadsley's user avatar
5 votes

$\mathbb{Z}G$ (left) Noetherian$\Rightarrow$ $\ell^1(G)$ is a flat (right) $\mathbb{Z}G$-mod...

Here are a few observations that are too long for a comment but don't provide a full answer by any means. As Peter Samuelson observed left-right questions aren't significant in this setting since $\m …
Simon Wadsley's user avatar
5 votes
Accepted

Testing ideal membership in the Weyl algebra: a simple example

Following my nose gave the following argument. Writing $I$ be the left ideal generated by $x\partial^2$ and $x^3$ and using $\cdot$ to stress multiplication we get $$ x^2 \cdot x\partial^2 - \partia …
Simon Wadsley's user avatar
4 votes
Accepted

$R/I\cong R/\text{Ann}_R(R/I)$ but $I\neq\text{Ann}_R(R/I)$

You might as well assume that $\mathrm{Ann}_R(R/I)=0$ since if $S=R/\mathrm{Ann}_R(R/I)$ then $R/I\cong S$ as $R$-modules if and only if $S/(I/\mathrm{Ann}_R(R/I))\cong S$ as $S$-modules. So now the q …
Simon Wadsley's user avatar
4 votes
Accepted

Dual of a bimodule

Copied from comments as requested. There isn't enough context in the question but if you know that $B$ is a projective left $R$-module and nothing else there is a fair chance that you want $\mathrm{H …
Simon Wadsley's user avatar
3 votes
Accepted

Separable and finitely generated projective but not Frobenius?

Theorem 4.2 of On separable algebras over a commutative ring says that the answer is always yes.
Simon Wadsley's user avatar
2 votes

Localising a right Noetherian ring at a set of regular elements

It is not true that the right ring of fractions always exists in the setting you describe. An example where it does not can be found in section 2.1.7 of McConnell and Robson's book Noncommutative Noet …
Simon Wadsley's user avatar