Consider the following premises. For all x, if x drinks water, then x is taking a plane. There is at least one x for which x will not take a plane. For all x, x will drink water or x will not take a plane. Can we infer the following from them? If we can, name the inference rule being used: For all x, x will drink water.
 From the fact that for all x, x will drink water or x will not take a plane we can infer that for all x, if x takes a plane, then x is drinking water via universal rewriting. 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. Finally, from the fact that for all x, x will take a plane if and only if x will drink water, and that there is at least one x for which x will not take a plane we can infer that there is at least one x for which x will not drink water via existential biconditional elimination, which contradicts that For all x, x will drink water. Therefore, the answer is no.