So, this implies that the derivative of xd with respect to the p times the derivative of ps* with respect to a plus the derivative of xd with respect to k, have to derivate with respect to both things because there are two variables, is going to be equal to the derivative of xs with respect to p times the derivative of p* with respect to a way by the chain rule plus again, the derivative of x, x, xs, the quantity of supply with respect to a. 