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. 17 is in set B, so take out anything that is in set B. So you get the 5, the 3. See, the 12 is not in set B, so we can keep that in there.