Consider the following premises. For all x_18, if x_18 takes a plane, then x_18 is a politician. For all x_18, if x_18 were a politician, then x_18 is taking a plane. For all x_18, x_18 will take a plane. Can we infer the following from them? John is not a politician.
 From the fact that for all x_18, if x_18 were a politician, then x_18 is taking a plane, and that for all x_18, if x_18 takes a plane, then x_18 is a politician we can infer that for all x_18, x_18 is a politician if and only if x_18 will take a plane. From the fact that for all x_18, x_18 is a politician if and only if x_18 will take a plane we can infer that for all x_18, if x_18 takes a plane, then x_18 is a politician. Finally, from the fact that for all x_18, if x_18 takes a plane, then x_18 is a politician, and that for all x_18, x_18 will take a plane we can infer that for all x_18, x_18 is a politician, which contradicts that John is not a politician. Therefore, the answer is no.