# Problem with unpaired [] in math mode in comments [duplicate]

The following text is typeset correctly in a post, but it seems to be broken when posted in a comment. (Markdown somehow interprets left [ as beginning of a hyperlink).

Any concave function $f\colon[0,\infty)\to\mathbb R$ such that $f(0)=0$ is [subadditive](http://en.wikipedia.org/wiki/Subadditivity).

Any concave function $f\colon[0,\infty)\to\mathbb R$ such that $f(0)=0$ is subadditive.

I'm posting two comments below this post to illustrate this. I've tried this also in Formatting Sandbox and here's a screenshot:

(Of course this is not very important and it should be easy to circumvent this, when you notice the problem. I just thought I should mention such behavior here at meta, when I ran into it.)

• Any concave function $f\colon[0,\infty)\to\mathbb R$ such that $f(0)=0$ is subadditive. – Martin Sleziak Jun 28 '12 at 14:15
• Any concave function $f\colon[0,\infty]\to\mathbb R$ such that $f(0)=0$ is subadditive. – Martin Sleziak Jun 28 '12 at 14:15
• After seeing Zev's answer, the problem seems to be related to this: MathJax requires escaping of certain markdown symbols between single dollar signs. However, it is to some extent surprising that the behavior is different in a post and in a comment. – Martin Sleziak Jun 28 '12 at 15:03
• I've accepted Zev's answer. (It worked at the time when I posted this question.) It seems that in the meantime the things have changed, to find more recent information have a look at the duplicate question. – Martin Sleziak Oct 10 '13 at 18:44

I think that "escaping" the delimiters with a backslash, e.g. \[ and \), fixes the problem:

$\[0,\infty\)$  [google](http://www.google.com)


in a comment produces

• Test: $\[0,\infty\)$ [google](http://www.google.com) produces $\[0,\infty\)$ google. – Martin Sleziak Jun 28 '12 at 15:04

The mini-markdown in the comments is different from the full-blown markdown in the answer and it's optimized for efficiency even though this means we can't support all the features of normal markdown.

Please adopt a workaround if it is possible.

There are ways to make invisible close brackets. \vphantom] will usually do the trick, I imagine, as the previous open bracket will have made the line the same height this otherwise would. If you're desperate, \smash{\vphantom]} might work in a few more cases. There may be stronger ways I don't know about.

• Test: $[0,\infty)\vphantom]$ [google](http://www.google.com) produces $[0,\infty)\vphantom]$ google. – dfeuer Oct 10 '13 at 14:36