Consider the following premises. For all z_4, if z_4 plays squash, then z_4 is poor. For all z_4, if z_4 were poor, then z_4 is playing squash. There is at least one z_4 for which z_4 is not a janitor. For all z_4, z_4 will play squash if and only if z_4 is a janitor. Can we infer the following from them? For all z_4, z_4 is poor.
 From the fact that for all z_4, if z_4 were poor, then z_4 is playing squash, and that for all z_4, if z_4 plays squash, then z_4 is poor we can infer that for all z_4, z_4 is poor if and only if z_4 will play squash. From the fact that for all z_4, z_4 will play squash if and only if z_4 is a janitor, and that there is at least one z_4 for which z_4 is not a janitor we can infer that there is at least one z_4 for which z_4 will not play squash. Finally, from the fact that for all z_4, z_4 is poor if and only if z_4 will play squash, and that there is at least one z_4 for which z_4 will not play squash we can infer that there is at least one z_4 for which z_4 is not poor, which contradicts that For all z_4, z_4 is poor. Therefore, the answer is no.