This answer addresses the same problem. It is best to insert a space every so often into MathJax in a comment so that there are 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.
