After completing exercise 3, modify the lookup: method from exercise 2 to perform a search on all the fields of an address card. Can you think of a way to design your AddressCard and AddressBook...

After completing exercise 3, modify the lookup: method from exercise 2 to perform a search on all the fields of an address card. Can you think of a way to design your AddressCard and AddressBook classes so that the latter does not have to know all the fields stored in the former?