Consider the following premises. For all x, if x were an office clerk, then x is taking a plane. For all x, if x drinks water, then x is taking a plane. For all x, if x takes a plane, then x is drinking water. Can we infer the following from them? If we can, name the inference rule being used: For all x, if x were an office clerk, then x is drinking water.
 From the fact that for all x, if x takes a plane, then x is drinking water, and that for all x, if x drinks water, then x is taking a plane we can infer that for all x, x will take a plane if and only if x will drink water via universal biconditional introduction. From the fact that for all x, x will take a plane if and only if x will drink water we can infer that for all x, if x takes a plane, then x is drinking water via universal biconditional elimination. Finally, from the fact that for all x, if x were an office clerk, then x is taking a plane, and that for all x, if x takes a plane, then x is drinking water we can infer that for all x, if x were an office clerk, then x is drinking water via universal transitivity. Therefore, the answer is yes.