What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Name the inference rule being used: For all z_1, z_1 is a taxi driver or z_1 is not poor. For all z_1, z_1 is not a taxi driver. For all z_1, if z_1 were a taxi driver, then z_1 is poor.
For all z_1, if z_1 were poor, then z_1 is a taxi driver can be inferred via the universal rewriting rule.