Consider the following premises. For all x_9, if x_9 makes tea, then x_9 is writing a letter. For all x_9, x_9 will take a plane or x_9 will play tennis. There is at least one x_9 for which x_9 will write a letter if and only if x_9 will play tennis. For all x_9, x_9 will not take a plane. Can we infer the following from them? For all x_9, x_9 will not write a letter.
 From the fact that for all x_9, x_9 will take a plane or x_9 will play tennis, and that for all x_9, x_9 will not take a plane we can infer that for all x_9, x_9 will play tennis. From the fact that for all x_9, x_9 will play tennis we can infer that for all x_9, x_9 will play tennis or x_9 will make tea. From the fact that there is at least one x_9 for which x_9 will write a letter if and only if x_9 will play tennis we can infer that there is at least one x_9 for which if x_9 plays tennis, then x_9 is writing a letter. Finally, from the fact that there is at least one x_9 for which if x_9 plays tennis, then x_9 is writing a letter, that for all x_9, if x_9 makes tea, then x_9 is writing a letter, and that for all x_9, x_9 will play tennis or x_9 will make tea we can infer that there is at least one x_9 for which x_9 will write a letter, which contradicts that For all x_9, x_9 will not write a letter. Therefore, the answer is no.