The derivative with respect to x of y squared. And the realization here is to just apply the chain rule. If we're taking the derivative with respect to x of this something, we just have to take the derivative, let me make it clear, we're just gonna take the derivative of our something, the derivative of y squared, that's what we're taking, you can kind of view that as a function, with respect to y, with respect to y, and then multiply that times the derivative of y, the derivative of y with respect to x. 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.