And the key here is to really break it down, work on the parentheses, the stuff in the parentheses first, just as you would do if you were trying to parse a traditional mathematical statement. And then it should hopefully make a little bit of sense. So a good place to start might be to try to figure out what is the relative complement of C in B. Or another way of thinking about it is what is B minus C? What is B if you take out all the stuff with C in it? So let me write this down. The relative complement of C in B, or you could call this B minus C, this is all the stuff in B with all the stuff in C taken out of it.