human
Here's a good function header given the following:
I wrote the below code

    def doit(C):
        r = ((z * C.diff(z)) + (C * M))
        r = r.applyfunc(make_simp(z))
        return r
    return doit

What's a good function header?
assistant
#Here's a good function header.

def make_derivative_operator(M, z):