Consider the following premises. For all x_15, x_15 will climb a mountain or x_15 will not drive a car. For all x_15, x_15 is a server. For all x_15, if x_15 climbs a mountain, then x_15 is driving a car. For all x_15, if x_15 takes a plane, then x_15 is not a server. There is at least one x_15 for which x_15 will take a plane if and only if x_15 will climb a mountain. Can we infer the following from them? If we can, name the inference rule being used: There is at least one x_15 for which x_15 will not drive a car.
 From the fact that for all x_15, if x_15 takes a plane, then x_15 is not a server, and that for all x_15, x_15 is a server we can infer that for all x_15, x_15 will not take a plane via universal modus tollens. From the fact that for all x_15, x_15 will climb a mountain or x_15 will not drive a car we can infer that for all x_15, if x_15 drives a car, then x_15 is climbing a mountain via universal rewriting. From the fact that for all x_15, if x_15 drives a car, then x_15 is climbing a mountain, and that for all x_15, if x_15 climbs a mountain, then x_15 is driving a car we can infer that for all x_15, x_15 will drive a car if and only if x_15 will climb a mountain via universal biconditional introduction. From the fact that there is at least one x_15 for which x_15 will take a plane if and only if x_15 will climb a mountain, and that for all x_15, x_15 will not take a plane we can infer that there is at least one x_15 for which x_15 will not climb a mountain via existential biconditional elimination. Finally, from the fact that for all x_15, x_15 will drive a car if and only if x_15 will climb a mountain, and that there is at least one x_15 for which x_15 will not climb a mountain we can infer that there is at least one x_15 for which x_15 will not drive a car via existential biconditional elimination. Therefore, the answer is yes.