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Matrices not rendered correctly

I'm trying to display old-style notations for combinations, that is, ${}_nC_r$ for the thing now typically written $n\choose r$. To get the "$n$" here you must put a subscript on an empty expression, thus: $\$${}_nC_r$\$$.

I can't get this to work correctly when the trailing subscript is multi-character. If I want $n\choose 11$ and put the braces where I'd expect them, it comes out like this: ${}_nC_{11}$. Note that I didn't quote anything; the system simply refuses to interpret the TeX.

There's no problem if the first subscript is multi-character ${}_{11}C_9$ works OK.

It looks like the problem is that one or t'other underscore obscures the trailing dollar sign, so math mode isn't exited properly. If I try the $n\choose 11$ example again and include another math expression before the next paragraph break, it comes out like this: ${}_nC_{11}$ is zero by definition when $n<11$.


marked as duplicate by kennytm Nov 2 '10 at 16:57

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  • $\begingroup$ Use backslash, e.g. {}\\_nC\\_{11} -> ${}\_nC\_{11}$ to avoid Markdown interpreting the underscores as italic. $\endgroup$ – kennytm Nov 2 '10 at 17:06
  • $\begingroup$ @KennyTM, why can't we escape text inside of the dollar signs like on MO (by allowing mathJax to render inside of code tags)? $\endgroup$ – 97832123 Nov 2 '10 at 21:54
  • $\begingroup$ @978: that's what meta.math.stackexchange.com/questions/551/… is about, meh. $\endgroup$ – kennytm Nov 2 '10 at 22:26
  • $\begingroup$ @KennyTM: I find your support for the status-quo incredibly frustrating. It's not hard to do, so just help us campaign for it. $\endgroup$ – 97832123 Nov 3 '10 at 7:01
  • $\begingroup$ @978: What else you want to do? I've already filed a feature-request to mimic the MO behavior. I do not control the back-end, if the admins at SO Inc. decided it's not an issue there's nothing we can do. $\endgroup$ – kennytm Nov 3 '10 at 7:03
  • $\begingroup$ @KennyTM: Did they decide that? If so, we should just keep bugging them about it until they do something (that is what we can do!). $\endgroup$ – 97832123 Nov 3 '10 at 12:01

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