If mathcode is used to typeset e and i upright, how to force it italics again?

Question

I'm using \mathcode"69"69 in the preamble, as proposed in a comment in this question, to automatically typeset e and i upright in mathematical equations.

The question is, is there a way to get an italics i f.ex. as an index in math mode later? If so, how?

I tried $\mathit{i}$, which doesn't work.

Answer 1

Commands can be defined using the old mathcode settings for i and e:

\documentclass{article}

\mathchardef\iti=\mathcode`\i
\mathchardef\ite=\mathcode`\e
\mathcode`\i=`\i
\mathcode`\e=`\e

\begin{document}

\begin{displaymath}
4 + 7i = 4e^{10} + b_\iti^\ite
\end{displaymath}

\end{document}