Consider the following premises. For all x_4, x_4 is a server if and only if x_4 will drink water. For all x_4, x_4 will not drink water. For all x_4, x_4 is a server if and only if x_4 is poor. Can we infer the following from them? If we can, name the inference rule being used: For all x_4, x_4 is not poor.
 From the fact that for all x_4, x_4 is a server if and only if x_4 will drink water, and that for all x_4, x_4 will not drink water we can infer that for all x_4, x_4 is not a server via universal biconditional elimination. Finally, from the fact that for all x_4, x_4 is a server if and only if x_4 is poor, and that for all x_4, x_4 is not a server we can infer that for all x_4, x_4 is not poor via universal biconditional elimination. Therefore, the answer is yes.