Consider the following premises. For all x_9, if x_9 were a janitor, then x_9 is taking a plane. For all x_9, x_9 will write a letter if and only if x_9 will take a plane. For all x_9, if x_9 writes a letter, then x_9 is running. For all x_9, if x_9 goes running, then x_9 is a janitor. Can we infer the following from them? There is at least one x_9 for which if is not true that x_9 will write a letter if and only if x_9 will go running.
 From the fact that for all x_9, if x_9 goes running, then x_9 is a janitor, and that for all x_9, if x_9 were a janitor, then x_9 is taking a plane we can infer that for all x_9, if x_9 goes running, then x_9 is taking a plane. From the fact that for all x_9, x_9 will write a letter if and only if x_9 will take a plane we can infer that for all x_9, if x_9 takes a plane, then x_9 is writing a letter. From the fact that for all x_9, if x_9 goes running, then x_9 is taking a plane, and that for all x_9, if x_9 takes a plane, then x_9 is writing a letter we can infer that for all x_9, if x_9 goes running, then x_9 is writing a letter. Finally, from the fact that for all x_9, if x_9 writes a letter, then x_9 is running, and that for all x_9, if x_9 goes running, then x_9 is writing a letter we can infer that for all x_9, x_9 will write a letter if and only if x_9 will go running, which contradicts that There is at least one x_9 for which if is not true that x_9 will write a letter if and only if x_9 will go running. Therefore, the answer is no.