We've just setup some LaTeX support, thanks to the great work of "OlegK", the author of the "SELaTeX" project, and John Forkosh, the author of the mathtex project.

You'll see a sidebar on the right, which allows you to type LaTeX and provides a real-time preview. When you're done, you can copy and paste the code over to your post. The code it produces is MarkDown syntax for an image tag. It generates alt-text containing the original LaTeX, so you can edit and see other people's source if you need to.

We've modified the original SELaTeX code in order to use our own LaTeX renderer, rather than the one over at codecogs.com. It's possible we'll have issues with this, so please report any problems.

We are well aware of the insufficiencies of this solution. In particular, it would be lovely to provide MathML to browsers that can handle it, but for now that's beyond us. It would be great to be able to write LaTeX inline in your post, rather than having to jump to the sidebar, but that will have to wait on support from FogCreek, the makers of the StackExchange software. Anyway -- perfect is the enemy of good, so for now we're going with this.

It looks a little wonky if you use latex with a sentence: http://mathoverflow.net/questions/4062/can-homgpg-h-fail-to-be-representable-for-affine-algebraic-groups.

I know this is just being really picky, but is it possible to call this something more accurate than "LaTeX"? It's LaTeX mathematics mode, so you don't need to put in the dollars, and ordinary text commands may or may not work, depending on whether or not they are valid in mathematics mode.

But apart from that, that's a great feature to have.

Yes and No. In the Grand Scheme of Things, then no, it doesn't really matter. In the scheme of trying to make the site as useful as possible, then yes, it does matter. You can't type arbitrary LaTeX syntax into that box, it doesn't work. You can type a simplified subset of LaTeX. Exactly what that subset is, I don't know. A little experimenting showed that it stripped out certain commands, but not others.

The preview feature mitigates this a little, since it's obvious that stuff isn't appearing as one would expect, but it's still not technically correct to say that you can use LaTeX input.

@David Brown: The problem is that the underscores in the alt text are special Markdown characters. When you have two underscores on a line, everything between them gets italicized. Since this is the "intended" behavior, I don't think Fog Creek will fix it, but we can. We just have to decide how to. The problem is that if we change the alt text (e.g. by escaping all the underscores and stars), then it becomes slightly harder to edit the source. I think this is a tolerable price to pay. I'll see if I can modify the javascript to escape underscores and stars. For now, you can escape them manually, like I did in your question.

@Andrew: I'd be happy to use a more accurate name. I get the same little twinge of annoyance every time I see (or use) the term "LaTeX", but I don't see a good way around it without constantly launching into explanations about how it isn't really LaTeX.

@fedja: sometimes, the box doesn't appear for me, but it appears after reloading the page. Does this work for you?

Great work! Would it be possible to make it perfect by adding a button to paste text from the right box to the left in a single click?

Re: the underlying bug in Markdown for handling underscores and stars in the alt text.

Does anyone know how the Markdown code is maintained? Does FogCreek use a standard distribution of Markdown, or have they forked. Can we just submit bug reports and/or patches to someone further upstream than FogCreek?

@Scott: here's the Javascript: document.getElementById("wmd-input").value += ' ' +document.getElementById("code-box").value + ' '

I wasn't able to paste a javascript link here, but you can prefix above with javascript: and put into your bookmarks. Clicking on this bookmark will copy text from the code box to the edit box. Tested: Safari 4.

@hanche Flott! Jeg viste ikke denne løsningen. Jeg lærer nye ting hver dag.

I've just added a comment to the first link mentioning the issue and added the remark about it being fixed in PHP markdown to the second.

Depending on which page I'm on, I either get the jsMath banner or the "LaTeX in the box" banner.

Also, what's the default: jsMath or LaTeX-via-images?

Images inserted from the side bar don't appear in the mathoverflow.net/questions page.

Example: look at this question. The author apparently used the sidebar to create the symbol C^infty. If you bring up the "all questions" page and scroll until you see this question (page 1 at the moment), you see

Given a compact smooth manifold $M$, it's relatively well known that $(M)$ determines $M$ up to diffeomorphism.

That symbol "(M)" should be "C^infty(M)".