Consider the following premises. For all x_3, x_3 will play squash. For all x_3, if x_3 plays squash, then x_3 is taking a plane. There is at least one x_3 for which x_3 will sleep if and only if x_3 will take a plane. Can we infer the following from them? For all x_3, x_3 will not sleep.
 From the fact that there is at least one x_3 for which x_3 will sleep if and only if x_3 will take a plane we can infer that there is at least one x_3 for which if x_3 takes a plane, then x_3 is sleeping. From the fact that for all x_3, if x_3 plays squash, then x_3 is taking a plane, and that for all x_3, x_3 will play squash we can infer that for all x_3, x_3 will take a plane. Finally, from the fact that there is at least one x_3 for which if x_3 takes a plane, then x_3 is sleeping, and that for all x_3, x_3 will take a plane we can infer that there is at least one x_3 for which x_3 will sleep, which contradicts that For all x_3, x_3 will not sleep. Therefore, the answer is no.