So f prime of x, another way of expressing it, and I'll use it with more of the differential notation. You could view this as the derivative of, well, I'll write it a couple of different ways. You could view it as the derivative of v, the derivative of v with respect to u, I want to get the colors right, the derivative of v with respect to u, that's what this thing is right over here, times the derivative of u with respect to x. So times the derivative of u with respect to x. And just to make clear, so you're familiar with the different notations you'll see in different textbooks, this is this right over here, just using different notations, and this is this right over here. So let's actually evaluate these things. You're probably tired of just talking in the abstract.