Consider the following premises. For all x_4, x_4 will play squash or x_4 will play tennis. For all x_4, if x_4 plays tennis, then x_4 is rich. For all x_4, x_4 is rich if and only if x_4 will play squash. Can we infer the following from them? There is at least one x_4 for which x_4 is not rich.
 From the fact that for all x_4, x_4 is rich if and only if x_4 will play squash we can infer that for all x_4, if x_4 plays squash, then x_4 is rich. Finally, from the fact that for all x_4, if x_4 plays squash, then x_4 is rich, that for all x_4, if x_4 plays tennis, then x_4 is rich, and that for all x_4, x_4 will play squash or x_4 will play tennis we can infer that for all x_4, x_4 is rich, which contradicts that There is at least one x_4 for which x_4 is not rich. Therefore, the answer is no.