So it outputs the natural log of the square root of x. If we wanted to write v with x as an input, we would just say, well, that's just the natural log. That is just the natural log of x. And as you can see here, f of x, and I color-coded it ahead of time, is equal to, f of x, f of x is equal to the natural log of the square root of x. So that is v of the square root of x, or v of u of x. So it is a composition, which tells you that, okay, if I'm trying to find the derivative here, the chain rule is going to be very, very, very, very useful. And the chain rule tells us that f prime of x is going to be equal to the derivative of, you can view it as the outside function, with respect to this inside function.