Consider the following premises. There is at least one x_1 for which if x_1 drinks water, then x_1 is poor. For all x_1, x_1 will drink water if and only if x_1 is an office clerk. For all x_1, x_1 is not poor. Can we infer the following from them? If we can, name the inference rule being used: There is at least one x_1 for which x_1 is not an office clerk.
 From the fact that there is at least one x_1 for which if x_1 drinks water, then x_1 is poor, and that for all x_1, x_1 is not poor we can infer that there is at least one x_1 for which x_1 will not drink water via existential modus tollens. Finally, from the fact that for all x_1, x_1 will drink water if and only if x_1 is an office clerk, and that there is at least one x_1 for which x_1 will not drink water we can infer that there is at least one x_1 for which x_1 is not an office clerk via existential biconditional elimination. Therefore, the answer is yes.