Comment 12 for bug 1814286

According to [1], \def and \let should both work fine with mathjax

[1]http://docs.mathjax.org/en/latest/tex.html#tex-commands

I think this has something more to do with the the delimiters [2]. Testing now, will report back.

[2] http://docs.mathjax.org/en/latest/tex.html#defining-tex-macros