> I wonder whether this should be done in Polys. so rather than
> penalize all expr by having to do this check, make Polys provide a
> method named ``coeff` that converts itself to expr and then applies
> the coeff method. Any thoughts?

Yes, maybe. At least we can try.

But maybe we can even find the answer to a coeff()
call without going to expr first?

Maybe this would duplicated to much code ...

I don't know what's best here.