You could view this as B subtracted from A, or you could view this as the relative complement of set B in A. And we're going to talk a lot more about complements in the future, but the complement is the things that are not in B. And so this is saying, look, what are all of the things that are not in B? So you could say, what are all of the things not in B but are in A? So once again, if you said all of the things that aren't in B, then you're thinking about all of the numbers in the whole universe that aren't 17, 19, or 6. And actually, you could even think broader. You're not even just thinking about numbers.