Consider the following premises. For all x_9, x_9 is a police officer if and only if x_9 will play squash. For all x_9, x_9 will work. There is at least one x_9 for which if x_9 were a police officer, then x_9 is not driving a car. For all x_9, if x_9 works, then x_9 is driving a car. Can we infer the following from them? If we can, name the inference rule being used: There is at least one x_9 for which x_9 will not play squash.
 From the fact that for all x_9, if x_9 works, then x_9 is driving a car, and that for all x_9, x_9 will work we can infer that for all x_9, x_9 will drive a car via universal modus ponens. From the fact that there is at least one x_9 for which if x_9 were a police officer, then x_9 is not driving a car, and that for all x_9, x_9 will drive a car we can infer that there is at least one x_9 for which x_9 is not a police officer via existential modus tollens. Finally, from the fact that for all x_9, x_9 is a police officer if and only if x_9 will play squash, and that there is at least one x_9 for which x_9 is not a police officer we can infer that there is at least one x_9 for which x_9 will not play squash via existential biconditional elimination. Therefore, the answer is yes.