On Mathematics.SE the behavior is different: $a < b$. This becomes a problem when one copies formulas from a comment into an answer, as mentioned here. In the HTML source of comments,
< is replaced by
Can MathJax be configured to render
$a < b$on this site?
Edit: I just came across another place where this issue arises:
Edit 2: I found the problem: SE escapes the ampersand in
< turning the string into
&lt;. And that is an HTML entity that MathJax does not support in present.
Either MathJax should interpret
<, or SE should stop messing up
Related threads, all marked with status-completed: