Consider the following premises. For all y_4, if y_4 plays tennis, then y_4 is playing squash. For all y_4, if y_4 plays squash, then y_4 is playing tennis. There is at least one y_4 for which y_4 will not play squash. Can we infer the following from them? There is at least one y_4 for which y_4 will not play tennis.
 From the fact that for all y_4, if y_4 plays squash, then y_4 is playing tennis, and that for all y_4, if y_4 plays tennis, then y_4 is playing squash we can infer that for all y_4, y_4 will play squash if and only if y_4 will play tennis. From the fact that for all y_4, y_4 will play squash if and only if y_4 will play tennis we can infer that for all y_4, if y_4 plays tennis, then y_4 is playing squash. Finally, from the fact that for all y_4, if y_4 plays tennis, then y_4 is playing squash, and that there is at least one y_4 for which y_4 will not play squash we can infer that there is at least one y_4 for which y_4 will not play tennis. Therefore, the answer is yes.