[This answer](http://meta.math.stackexchange.com/a/3968) addresses the same problem. It is best to insert a space every so often into MathJax in a comment so that there is not 80 characters unbroken by spaces.

In the comment in consideration,

    $$TV(f_{[x,x_0]})=TV(f_{[x_1,x_0]})-TV(f_{[x_1,x]})<(V+\epsilon/2)-(V-|f(x)-f(x_

is 80 characters. The two unicode spaces are inserted between the underscore and the zero, interrupting the MathJax.