But then if you took the derivative of both sides of this, what would you get? Let me do that. So if we take the derivative of both sides of this, d dx on the left-hand side, d dx on the right-hand side, and I think you see where this is going. You're essentially going to get a version of that. The left-hand side, use the chain rule. You're going to get f prime of h of x, f prime of h of x times h prime of x, comes straight out of the chain rule, is equal to, is equal to the derivative of x, is just going to be equal to one. And then you divide both sides by f prime of h of x, and you get our original property there.