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 y_4, y_4 will not drive a car. For all y_4, if y_4 drives a car, then y_4 is poor. There is at least one y_4 for which if y_4 were poor, then y_4 is driving a car.
There is at least one y_4 for which y_4 is not poor can be inferred via the existential modus tollens rule. There is at least one y_4 for which y_4 is poor if and only if y_4 will drive a car can be inferred via the existential biconditional introduction rule. There is at least one y_4 for which y_4 will drive a car if and only if y_4 is poor can be inferred via the existential biconditional introduction rule.