Here is my problem: I would like, as in some old maths books, use oldstyle figures as coefficients in math formulae – say in display- and textstyle, but lining figures for indices and exponents – say in script- and scriptscriptstyle. I'm not sure this is strictly equivalent, though. I guess that the use of the
\mathchoice command would be useful, but I really don't know how to use it.
Does anyone know how to achieve this automatically?
Added: I forgot to say that a solution should work with any math font. It happens that the proposed solution, which works perfectly well with default TeX math fonts doesn't work with MinionPro. Maybe a specific problem of MinionPro?