Let me do the u of x in blue. v prime of u of x times u prime of x. Well, what is v prime of u of x? We know what v prime of x is. If we wanted to do v prime of u of x, we would just replace wherever we see an x with the u of x. So this is going to be equal to v prime of u of x. And you just use it, you're taking the derivative of the green function with respect to the blue function.