What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? For all z, if z were a cashier, then z is a server. There is at least one z for which if z were a server, then z is a cashier. For all z, if z were a cashier, then z is a server.
There is at least one z for which z is a server if and only if z is a cashier. There is at least one z for which z is a server if and only if z is a cashier. There is at least one z for which z is a cashier if and only if z is a server. There is at least one z for which z is a cashier if and only if z is a server.