Consider the following premises. There is at least one x_9 for which x_9 will take a plane if and only if x_9 is a taxi driver. For all x_9, x_9 will take a plane if and only if x_9 is a carpenter. Can we infer the following from them? If we can, name the inference rule being used: There is at least one x_9 for which if x_9 were a carpenter, then x_9 is a taxi driver.
 From the fact that for all x_9, x_9 will take a plane if and only if x_9 is a carpenter we can infer that for all x_9, if x_9 were a carpenter, then x_9 is taking a plane via universal biconditional elimination. From the fact that there is at least one x_9 for which x_9 will take a plane if and only if x_9 is a taxi driver we can infer that there is at least one x_9 for which if x_9 takes a plane, then x_9 is a taxi driver via existential biconditional elimination. Finally, from the fact that for all x_9, if x_9 were a carpenter, then x_9 is taking a plane, and that there is at least one x_9 for which if x_9 takes a plane, then x_9 is a taxi driver we can infer that there is at least one x_9 for which if x_9 were a carpenter, then x_9 is a taxi driver via existential transitivity. Therefore, the answer is yes.