And then you say, fine, I'm going to give you a range around c that if you take any x within that range, your f of x is always going to fall in this range that you care about. And so you look at this. And obviously, we haven't explicitly defined this function. But you can even eyeball it the way this function is defined. It won't be that easy for all functions. But you look at it like this. And you say that this value, just the way it's drawn right over here, let's say that this is c minus 0.25.