Consider the following premises. For all x_11, if x_11 were happy, then x_11 is a server. For all x_11, if x_11 takes a plane, then x_11 is sleeping. For all x_11, x_11 is happy or x_11 is poor. For all x_11, if x_11 sleeps, then x_11 is a server. For all x_11, x_11 is poor if and only if x_11 will take a plane. Can we infer the following from them? If we can, name the inference rule being used: For all x_11, x_11 is a server.
 From the fact that for all x_11, x_11 is poor if and only if x_11 will take a plane we can infer that for all x_11, if x_11 were poor, then x_11 is taking a plane via universal biconditional elimination. From the fact that for all x_11, if x_11 takes a plane, then x_11 is sleeping, and that for all x_11, if x_11 sleeps, then x_11 is a server we can infer that for all x_11, if x_11 takes a plane, then x_11 is a server via universal transitivity. From the fact that for all x_11, if x_11 were poor, then x_11 is taking a plane, and that for all x_11, if x_11 takes a plane, then x_11 is a server we can infer that for all x_11, if x_11 were poor, then x_11 is a server via universal transitivity. Finally, from the fact that for all x_11, if x_11 were happy, then x_11 is a server, that for all x_11, if x_11 were poor, then x_11 is a server, and that for all x_11, x_11 is happy or x_11 is poor we can infer that for all x_11, x_11 is a server via universal disjunction elimination. Therefore, the answer is yes.