Consider the following premises. If John were a doctor, then Barbara is taking a plane. For all x_10, if x_10 takes a plane, then x_10 is happy. For all x_10, if x_10 were happy, then x_10 is taking a plane. Can we infer the following from them? If we can, name the inference rule being used: The fact that John were a doctor does not imply that Barbara is happy.
That contradicts the premises. Therefore the answer is no.