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 taxi driver. For all z, if z were a taxi driver, then z is a cashier.
For all z, z is a cashier if and only if z is a taxi driver. For all z, z is a taxi driver if and only if z is a cashier.