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 sailor. There is at least one z_1 for which if z_1 were a writer, then z_1 is not a nurse. For all z_1, z_1 is a nurse.
There is at least one z_1 for which z_1 is not a writer can be inferred via the existential modus tollens rule. For all z_1, z_1 is a sailor and z_1 is a nurse can be inferred via the universal conjunction rule. For all z_1, z_1 is a nurse and z_1 is a sailor can be inferred via the universal conjunction rule.