Consider the following premises. If Jessica takes a plane, then Jessica is a janitor. Jessica is not taking a plane. For all x_9, x_9 is a janitor if and only if x_9 will take a plane. Can we infer the following from them? If we can, name the inference rule being used: Jessica is not a janitor.
 From the fact that for all x_9, x_9 is a janitor if and only if x_9 will take a plane we can infer that Jessica is a janitor if and only if Jessica is taking a plane via universal instantiation. From the fact that Jessica is a janitor if and only if Jessica is taking a plane we can infer that if Jessica were a janitor, then Jessica is taking a plane via biconditional elimination. From the fact that if Jessica takes a plane, then Jessica is a janitor, and that if Jessica were a janitor, then Jessica is taking a plane we can infer that Jessica is taking a plane if and only if Jessica is a janitor via biconditional introduction. Finally, from the fact that Jessica is taking a plane if and only if Jessica is a janitor, and that Jessica is not taking a plane we can infer that Jessica is not a janitor via biconditional elimination. Therefore, the answer is yes.