Consider the following premises. For all y, y is a police officer if and only if y will drive a car. For all y, if y were a police officer, then y is driving a car. For all y, if y drives a car, then y is a police officer. Can we infer the following from them? If we can, name the inference rule being used: There is at least one y for which if is not true that y is a police officer if and only if y will drive a car.
 From the fact that for all y, y is a police officer if and only if y will drive a car we can infer that for all y, if y were a police officer, then y is driving a car via universal biconditional elimination. From the fact that for all y, if y drives a car, then y is a police officer, and that for all y, if y were a police officer, then y is driving a car we can infer that for all y, y will drive a car if and only if y is a police officer via universal biconditional introduction. From the fact that for all y, y will drive a car if and only if y is a police officer we can infer that for all y, if y drives a car, then y is a police officer via universal biconditional elimination. Finally, from the fact that for all y, if y were a police officer, then y is driving a car, and that for all y, if y drives a car, then y is a police officer we can infer that for all y, y is a police officer if and only if y will drive a car via universal biconditional introduction, which contradicts that There is at least one y for which if is not true that y is a police officer if and only if y will drive a car. Therefore, the answer is no.