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_2, if z_2 drives a car, then z_2 is a doctor. For all z_2, if z_2 were a doctor, then z_2 is driving a car. There is at least one z_2 for which z_2 is a soldier if and only if z_2 will drive a car.
For all z_2, z_2 will drive a car if and only if z_2 is a doctor can be inferred via the universal biconditional introduction rule. For all z_2, z_2 is a doctor if and only if z_2 will drive a car can be inferred via the universal biconditional introduction rule. There is at least one z_2 for which if z_2 were a soldier, then z_2 is driving a car can be inferred via the existential biconditional elimination rule. There is at least one z_2 for which if z_2 drives a car, then z_2 is a soldier can be inferred via the existential biconditional elimination rule.