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