Consider the following premises. For all x_9, if x_9 takes a plane, then x_9 is running. For all x_9, x_9 is not fast. For all x_9, if x_9 were fast, then x_9 is running. For all x_9, x_9 is fast if and only if x_9 will go running. Can we infer the following from them? If we can, name the inference rule being used: For all x_9, x_9 will not take a plane.
 From the fact that for all x_9, x_9 is fast if and only if x_9 will go running we can infer that for all x_9, if x_9 goes running, then x_9 is fast via universal biconditional elimination. From the fact that for all x_9, if x_9 were fast, then x_9 is running, and that for all x_9, if x_9 goes running, then x_9 is fast we can infer that for all x_9, x_9 is fast if and only if x_9 will go running via universal biconditional introduction. From the fact that for all x_9, x_9 is fast if and only if x_9 will go running, and that for all x_9, x_9 is not fast we can infer that for all x_9, x_9 will not go running via universal biconditional elimination. Finally, from the fact that for all x_9, if x_9 takes a plane, then x_9 is running, and that for all x_9, x_9 will not go running we can infer that for all x_9, x_9 will not take a plane via universal modus tollens. Therefore, the answer is yes.