We're assuming that y does change with respect to x. Y is not some type of a constant that we're writing just in abstract terms. So we're taking the derivative of this whole thing with respect to y. Once again, just the chain rule. And then we're taking the derivative of y with respect to x. It might be a little bit clearer if you kind of thought of it as the derivative with respect to x of y as a function of x. Y as a function of x. This might be, or y as a function of x squared, which is essentially another way of writing what we had here. This might be a little bit clearer in terms of the chain rule.