Linear equations over skewfields were studied in

- Oystein Ore,
*Linear equations in non-commutative fields*, Ann. Math.**32**:3 (1931) 463–477 doi

and more lately in the theory of quasideterminants, see there.

]]>I did end up editing *linear equation* a bit more last week. Looks like I am not going to touch it further for the time being.

I’m just asking questions, Urs. But I can wait. No argument here either.

]]>Hey Todd,

from #2 I gather you don’t want a long argument, and I don’t want it either. So far it’s a stub entry, it’s just something I happened to produce late at night one day. If nobody else feels like working on it, I’ll expand it next week to full beauty and then announce it again.

]]>I’d think the plan for nLab entries with titles like “linear equation” should be universal: give an elementary introduction first

Ostensibly we agree then. If I were commissioned to write an elementary introduction, I would be inclined to write something extremely simple, like “in the context of modules $M$, $N$ over a commutative ring $R$, a **linear equation** is an equation of the form $f = g$ where $f, g \in Mod_R(M, N)$.” (That’s just an example.) But since that kind of utterance is very close to being self-evident, the main question would be: what’s the point or goal of such an article? What is it that one really wants to say here? That’s why I’m trying to draw you out.

My earlier complaint was that a universal, elementary introduction (and especially the “Idea” section) should state things very simply, and avoid things like type-theoretic jargon with turnstiles and type declarations and so on (which is probably not the real point of the article anyway, and is probably distracting or confusing). What’s the point of the article?

And let me ask again, why did you want to restrict attention to maps of the form $f = K \otimes_R N$ where $K$ is an $R$-linear map $R^m \to R^n$?

]]>I have started *syzygy*. But let’s discuss that in it’s thread.

I had noted the grey link to identity among the relations and thus to homotopy syzygy and homological szyzgy. Creating those is on my list of things to do. I am not sure of the direction that Urs is thinking of for syzygy and equation, but the non-Abelian group theoretic ideas of Ronnie, Loday, Kapranov etc. may be useful and I can add material on these if and when it is needed. (There is stuff in the Menagerie, though probably not in the version I have available from my pages in the Lab.) Of course, these are non linear syzygies in general.

]]>are you planning to say something about syzygy

Yes, that’s where I was headed re projective resolutions. But then I definitely ran out of steam, being distracted by a few other things.

I might like to see what plans you have for this article first,

I’d think the plan for $n$Lab entries with titles like “linear equation” should be universal: give an elementary introduction first and then flesh out the category-theoretic and higher-category theoretic aspects.

But don’t worry if you don’t feel like getting into this and just wanted to point out that the current version is a stub. I’ll get to this more seriously by next week. But now I first have to take care of one last round of polishing *mapping cone* and then completing the entries on the diagram-chasing lemmas.

Okay, thanks. I might like to see what plans you have for this article first, before attempting to rework it in any way. One thing I don’t understand yet is why attention is being constrained to $R$-module maps of the form $K \otimes_R N: R^m \otimes_R N \to R^n \otimes_R N$.

To ask it more encouragingly, perhaps: are you planning to say something about syzygy in this article? Zoran once created a gray link to syzygy that has yet to be written.

]]>No argument here. I left the entry unfinished. Am tired now. Feel free to rework.

]]>I personally don’t think it’s a good idea to launch in with the type-theoretic notation right in the Idea section. It will look intimidating or rebarbative to many. At the same time, I hesitate to even say so, because I fear a long argument ahead.

]]>I finally started *linear equation*. But am too tired now to really do it justice…