That means that the function is increasing over that interval. So if we just think about it here, over this whole region right over here, the function is clearly decreasing. Then the slope becomes zero right over here. And then the function starts increasing again, all the way until this point right over here. It hits zero, and then it goes, and the function starts decreasing. So we're going to, just this first constraint right over here, tells us it's going to be something in this interval right over there. And then they say where the second derivative is less than zero.