Consider the following premises. There is at least one x_3 for which x_3 will take a plane if and only if x_3 is a scientist. For all x_3, if x_3 takes a plane, then x_3 is not cooking. For all x_3, x_3 will cook. Can we infer the following from them? If we can, name the inference rule being used: There is at least one x_3 for which x_3 is not a scientist.
 From the fact that for all x_3, if x_3 takes a plane, then x_3 is not cooking, and that for all x_3, x_3 will cook we can infer that for all x_3, x_3 will not take a plane via universal modus tollens. Finally, from the fact that there is at least one x_3 for which x_3 will take a plane if and only if x_3 is a scientist, and that for all x_3, x_3 will not take a plane we can infer that there is at least one x_3 for which x_3 is not a scientist via existential biconditional elimination. Therefore, the answer is yes.