So this is one way of thinking about the difference between set A and set B. And when I've written it this way, this essentially says, give me the set of all of the objects that are in A with the things that are in B taken out of that set. So let's think about what that means. So what's in set A with the things that are in B taken out? Well, that means let's take set A and take out a 17, a 19, or take out the 17s, the 19s, and the 6s. So we're going to be left with, we're going to have the 5, we're going to have the 3. We're not going to have the 17 because we subtracted out set B.