So that works. But if we get negative ten, so the system decreases in entropy by negative ten, but the universe increases only by nine, then we get negative ten plus nine will give you negative one, a negative number, a violation of the second law of thermodynamics. And this basically tells us that if the entropy of the system decreases, then the entropy of the surroundings must increase by the same amount or greater. You can never increase by less. Okay, now let's look at these isolated systems. We're going to define entropy in a different way.