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?

  • $\begingroup$ Can you provide me with links to a few examples of this? $\endgroup$ Jun 27, 2013 at 15:38
  • $\begingroup$ mathoverflow.net/questions/133168/generalized-basis/… (you see the \left\\{ does no longer work) $\endgroup$
    – The User
    Jun 27, 2013 at 15:46
  • $\begingroup$ mathoverflow.net/questions/130712/… (the large formula on the top is broken) $\endgroup$
    – The User
    Jun 27, 2013 at 15:47
  • $\begingroup$ @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. $\endgroup$
    – user9072
    Jun 27, 2013 at 20:48

2 Answers 2


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.

  • $\begingroup$ Not sure if it's the same problem but something happened to backslashes in Tom Goodwillie's answer here - mathoverflow.net/a/29570/2000 $\endgroup$ Jun 28, 2013 at 2:18
  • $\begingroup$ I have compared Toms answer post pre / post migrations and can confirm that this post was not impacted by the migration. $\endgroup$ Jun 28, 2013 at 2:44
  • $\begingroup$ 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. $\endgroup$ Jun 28, 2013 at 2:52
  • 1
    $\begingroup$ I specifically targeted \\{ and \\} in the last batch of updates. This means must mean there are more cases where \\ was used. $\endgroup$ Jun 28, 2013 at 3:01
  • $\begingroup$ 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? $\endgroup$ Jun 28, 2013 at 3:04
  • 1
    $\begingroup$ Yes, exactly - double backslashes were hidden from view in SE 1.0. $\endgroup$ Jun 28, 2013 at 3:06
  • $\begingroup$ Wouldn't a double backslash followed by letters show up as a single backslash followed by letters in 1.0? $\endgroup$ Jun 28, 2013 at 3:13
  • $\begingroup$ The spurious backslash is not in this archived version - web.archive.org/web/20130606041618/http://mathoverflow.net/… $\endgroup$ Jun 28, 2013 at 3:19
  • $\begingroup$ 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. $\endgroup$ Jun 28, 2013 at 3:35
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    $\begingroup$ @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. $\endgroup$ Jun 28, 2013 at 10:45
  • $\begingroup$ @EmilJeřábek: Ah! Right, that makes sense. Hopefully there are not too many such typos since these would be tricky to distinguish from the rest. $\endgroup$ Jun 28, 2013 at 11:58
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    $\begingroup$ 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 \. $\endgroup$ Jun 28, 2013 at 12:12
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    $\begingroup$ And as pointed out in meta.mathoverflow.net/questions/263, \\\ and \\\\ should be simplified to \\. $\endgroup$ Jun 28, 2013 at 15:22
  • $\begingroup$ @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. $\endgroup$ Sep 7, 2013 at 11:49

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


  • $\begingroup$ Wow. That LaTeX is so badly written that I feel the need to take another shower... $\endgroup$
    – Asaf Karagila Mod
    Jun 28, 2013 at 19:49
  • 3
    $\begingroup$ 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. $\endgroup$ Jun 28, 2013 at 21:25
  • $\begingroup$ At least one automatic conversion app tries to convert spacing in the original (presumably Word?) into \, spacing in LaTeX. $\endgroup$ Jun 29, 2013 at 13:02

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