It's not built into the site, but you can include LaTeX in comments and posts as an image; see the Less Wrong LaTeX Editor (built by our own John Maxwell using CodeCogs's LaTeX engine).
Example:
}(a)%20=%20\frac{n!}{2\pi%20i}%20\oint_\gamma%20\frac{f(z)}{(z-a)%5E{n+1}}\,%20dz)
Is there a way of editing equations created this way other than typing them all over again? Supposing you closed the browser tab with the original equation?
Apologies since I am almost sure this has been brought up before. Are there any plans for some sort of LateX or MathML functionality on the site?