Consider the following premises. For all x_1, x_1 is not curious. For all x_1, if x_1 were curious, then x_1 is a server. For all x_1, if x_1 were a server, then x_1 is curious. Can we infer the following from them? If we can, name the inference rule being used: For all x_1, x_1 is not a server.
 From the fact that for all x_1, if x_1 were a server, then x_1 is curious, and that for all x_1, if x_1 were curious, then x_1 is a server we can infer that for all x_1, x_1 is a server if and only if x_1 is curious via universal biconditional introduction. Finally, from the fact that for all x_1, x_1 is a server if and only if x_1 is curious, and that for all x_1, x_1 is not curious we can infer that for all x_1, x_1 is not a server via universal biconditional elimination. Therefore, the answer is yes.