 We can exemplify (ID) by letting x be {z} and y be z, in which case we have, as is intuitively correct, that {z} depends for its identity upon z, because there is a relation—namely, “being a member of the singleton set” (also known as the unit set function)—such that it is part of the essence of {z} that it is the singleton set of z. Accordingly, we may interpret the relation R more precisely on a case by case basis.