Consider the following premises. For all x_6, x_6 will drink water if and only if x_6 will play tennis. For all x_6, if x_6 plays tennis, then x_6 is not playing squash. For all x_6, x_6 will play squash. Can we infer the following from them? If we can, name the inference rule being used: There is at least one x_6 for which x_6 will drink water.
 From the fact that for all x_6, if x_6 plays tennis, then x_6 is not playing squash, and that for all x_6, x_6 will play squash we can infer that for all x_6, x_6 will not play tennis via universal modus tollens. From the fact that for all x_6, x_6 will drink water if and only if x_6 will play tennis we can infer that for all x_6, if x_6 drinks water, then x_6 is playing tennis via universal biconditional elimination. Finally, from the fact that for all x_6, if x_6 drinks water, then x_6 is playing tennis, and that for all x_6, x_6 will not play tennis we can infer that for all x_6, x_6 will not drink water via universal modus tollens, which contradicts that There is at least one x_6 for which x_6 will drink water. Therefore, the answer is no.