Consider the following premises. There is at least one x_5 for which if x_5 plays squash, then x_5 is drinking water. For all x_5, x_5 will drink water if and only if x_5 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_5 for which if x_5 drinks water, then x_5 is playing squash.
 From the fact that for all x_5, x_5 will drink water if and only if x_5 will play squash we can infer that for all x_5, if x_5 drinks water, then x_5 is playing squash via universal biconditional elimination. From the fact that for all x_5, if x_5 drinks water, then x_5 is playing squash, and that there is at least one x_5 for which if x_5 plays squash, then x_5 is drinking water we can infer that there is at least one x_5 for which x_5 will drink water if and only if x_5 will play squash via existential biconditional introduction. Finally, from the fact that there is at least one x_5 for which x_5 will drink water if and only if x_5 will play squash we can infer that there is at least one x_5 for which if x_5 drinks water, then x_5 is playing squash via existential biconditional elimination. Therefore, the answer is yes.