# Double backslashes

The “backslash-bug” from the old version is no longer there. You can simply write { and } to get $\{\}$. However, all the old questions and answers using \{ are now broken and look terrible: $\prod\\{Hello\\}$

Any idea how to solve this problem without removing all the double backslashes in all posts manually?

• Can you provide me with links to a few examples of this? – Geoff Dalgas Jun 27 '13 at 15:38
• mathoverflow.net/questions/133168/generalized-basis/… (you see the \left\\{ does no longer work) – The User Jun 27 '13 at 15:46
• mathoverflow.net/questions/130712/… (the large formula on the top is broken) – The User Jun 27 '13 at 15:47
• @GeoffDalgas since you were not notified by OP I thought I do so, not sure of this is useful. In any case, I agree this is an important matter as the formulas are so broken that they even get difficult to understand in several cases. – user9072 Jun 27 '13 at 20:48

I have finished a global update on posts that contain \\{ and \\} and rebaked all of these posts.

Please let me know if there are any other issues.

• Not sure if it's the same problem but something happened to backslashes in Tom Goodwillie's answer here - mathoverflow.net/a/29570/2000 – François G. Dorais Jun 28 '13 at 2:18
• I have compared Toms answer post pre / post migrations and can confirm that this post was not impacted by the migration. – Geoff Dalgas Jun 28 '13 at 2:44
• This is odd. Do you mean the weird double backslashes were there all along but didn't show previously? I think I would have fixed the weird double backslashes if it had been there when he originally answered my question. – François G. Dorais Jun 28 '13 at 2:52
• I specifically targeted \\{ and \\} in the last batch of updates. This means must mean there are more cases where \\ was used. – Geoff Dalgas Jun 28 '13 at 3:01
• But this one is rather odd. There was no need for double backslash there in 1.0 and it is a very noticeable error. So, I gather from your comparison, that the double backslash was there prior to migration but, for some very strange reason, wasn't visible then? – François G. Dorais Jun 28 '13 at 3:04
• Yes, exactly - double backslashes were hidden from view in SE 1.0. – Geoff Dalgas Jun 28 '13 at 3:06
• Wouldn't a double backslash followed by letters show up as a single backslash followed by letters in 1.0? – François G. Dorais Jun 28 '13 at 3:13
• The spurious backslash is not in this archived version - web.archive.org/web/20130606041618/http://mathoverflow.net/… – François G. Dorais Jun 28 '13 at 3:19
• Here is a query directly from the old SE 1.0 database: i.stack.imgur.com/xcw97.png I can't tell you why these backslashes didn't show up in the past due to the age of the SE 1.0 codebase and the many bugfixes that have been made since. I would however like to know if this is a sign of a larger issue. – Geoff Dalgas Jun 28 '13 at 3:35
• @François: I don’t think there is anything strange going on. The double backslash would be rendered as a single backslash by markdown, and then mathjax would interpret the resulting \sqrt in the expected way. In other words, \sqrt and \\sqrt were functionally equivalent in 1.0. The double backslash was not needed in this place, but it might have been just a typo which went unnoticed because it worked. – Emil Jeřábek supports Monica Jun 28 '13 at 10:45
• @EmilJeřábek: Ah! Right, that makes sense. Hopefully there are not too many such typos since these would be tricky to distinguish from the rest. – François G. Dorais Jun 28 '13 at 11:58
• I can’t imagine a legitimate use of a line break in an equation, it’s a safe bet that any \\ that does not appear in an environment like matrix, align, gather, cases, or in a \substack, should be simplified to \. – Emil Jeřábek supports Monica Jun 28 '13 at 12:12
• And as pointed out in meta.mathoverflow.net/questions/263, \\\ and \\\\ should be simplified to \\. – Emil Jeřábek supports Monica Jun 28 '13 at 15:22
• @Geoff, there's a lot of ruckus with people manually fixing double-backslashes since chrome disabled mathml. Is it possible to change all \\. to \. (. is any character) in math mode? I think that will introduce fewer errors than there are now. – François G. Dorais Sep 7 '13 at 11:49

Let me post an example that is still there... https://mathoverflow.net/a/131813/454 without correction it looks like this:

• Wow. That LaTeX is so badly written that I feel the need to take another shower... – Asaf Karagila Jun 28 '13 at 19:49
• Interesting, there are a few people who are apparently not fans of LaTeX's default spacing and insert \, everywhere. Of course, this leads to this kind of ridiculous results when combined with the fact that \blah and \\blah were functionally equivalent on 1.0, as Emil observed in another comment. I'm afraid the best procedure here is to edit manually. – François G. Dorais Jun 28 '13 at 21:25
• At least one automatic conversion app tries to convert spacing in the original (presumably Word?) into \, spacing in LaTeX. – Gerald Edgar Jun 29 '13 at 13:02