P1.5.7 Any subset statement may be interpreted as saying that some particular set is empty. Let D be a set of dogs, and let B R, and F be three subsets of D containing the black dogs, the retrievers, and the female dogs respectively. The statement B CR, for example, can be interpreted as "all the black dogs are retrievers" or "there are no black dogs who are not retrievers", that is, BUR= 0 For each of the following subset statements, identify the set that is claimed to be empty, both in English and in symbols: (a) BnF CR (b). FC ROB (c) B C RUF