But then let's get even closer. Let's say that point and that point, and then let's get even closer, and that point and that point, and then let's get even closer. And let's see what happens as the change in x approaches zero. And so using these d's instead of deltas, this was Leibniz's way of saying, hey, what happens if my changes in, say, x become close to zero? So this idea, this is known as sometimes differential notation, Leibniz's notation, is instead of just change in y over change in x, super small changes in y for a super small change in x, especially as the change in x approaches zero. And as you will see, that is how we will calculate the derivative. Now there's other notations.