Consider the following premises. For all x_12, x_12 will drive a car if and only if x_12 will take a plane. There is at least one x_12 for which x_12 will not drive a car. For all x_12, x_12 will take a plane if and only if x_12 is an electrician. Can we infer the following from them? If we can, name the inference rule being used: There is at least one x_12 for which x_12 is not an electrician.
 From the fact that for all x_12, x_12 will drive a car if and only if x_12 will take a plane we can infer that for all x_12, if x_12 takes a plane, then x_12 is driving a car via universal biconditional elimination. From the fact that for all x_12, if x_12 takes a plane, then x_12 is driving a car, and that there is at least one x_12 for which x_12 will not drive a car we can infer that there is at least one x_12 for which x_12 will not take a plane via existential modus tollens. Finally, from the fact that for all x_12, x_12 will take a plane if and only if x_12 is an electrician, and that there is at least one x_12 for which x_12 will not take a plane we can infer that there is at least one x_12 for which x_12 is not an electrician via existential biconditional elimination. Therefore, the answer is yes.