Evaluation under the derivative

Question

I give

depends(u,r)$
er : diff(u,r)$
er, u = r^2;

I am getting: d 2 (%o47) -- (r ) dr

However, I would like to obtain

2 r

How can force MAXIMA to evaluate that derivative?

Answer 1

I solved it! Use the keyword nouns:

depends(u,r)$
er : diff(u,r)$
er, nouns, u = r^2;