# A formula can't display properly in comment only

The term $\chi_{{}^{*}P}({}^{*}r)$ can display properly in the question, but when I paste it in a comment, it become something like:

which is the same as \chi_{{}^{}P}({}^{}r), when  eliminated.

The code is:

I've tried it on Firefox, and Chrome, and there's no difference. What is wrong?

• $\chi_{{}^{*}P}({}^{*}r)$ May 10, 2013 at 10:52
• Needs a space: $\chi_{{}^{}P} ({}^{}r)$ May 10, 2013 at 11:02
• @J.M. I'm not sure. There's no problem in displaying $\chi_P(r)$. But when I want to add a star to $P$ and $r$, it's kind of different. May 10, 2013 at 11:12
• Use \ast. $P\ast q$ May 10, 2013 at 11:15
• @J.M. Ah,yes!! That works. Thank you. May 10, 2013 at 11:17
• @J.M.: I think this is useful information. Why don't you promote your comment to an answer?
– robjohn Mod
May 10, 2013 at 12:59
• @rob, I was hoping Metta can answer his own question now. Oh well... May 10, 2013 at 13:00

Using \ast seems to work nicely, as \chi_{{}^{\ast}P}({}^{\ast}r) gives $\chi_{{}^{\ast}P}({}^{\ast}r)$
It looks like the interaction of Markdown being performed before MathJax runs, so the two stars end up being turned into marks for italics, and MathJax doesn't process the equation because it contains internal HTML. J.M.'s solution gets you around that. You could also use \* since that will prevent Markdown from processing the star (and also remove the \ so that it is just a * when MathJax sees it).