combine must be one of ('all', 'exp', 'base').

Raise code

        # break out the powers from c_powers now
        c_part = [Pow(b, ei) for b, e in c_powers.items() for ei in e]

        # we're done
        return expr.func(*(c_part + nc_part))

    else:
        raise ValueError("combine must be one of ('all', 'exp', 'base').")


def powdenest(eq, force=False, polar=False):
    r"""
    Collect exponents on powers as assumptions allow.

    Explanation """