And let me draw a little line here so that we don't get those two sides confused. And so we know from the chain rule, the derivative of y with respect to x, this is going to be, this is going to be the derivative of v with respect to u. Or we could call that v prime, v prime of u of x. v prime of u of x. 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.