I have a user interface problem that I hope isn't only solved by adding yet another option for authors to understand.

Student types a mathematical expression. We allow implicit multiplication, so `xy` is interpreted as `x*y`.
What to do about `pi`? Is it `p*i` or `π`?

I guess most of the time, you'd expect it to be interpreted as π. But you might be doing something with complex numbers, and `p*i` is really what you meant.
I suppose rendering π would at least give you a hint to add the * symbol