Consider the following premises. For all x_16, x_16 will drive a car. For all x_16, if x_16 were an electrician, then x_16 is sad. There is at least one x_16 for which if x_16 were sad, then x_16 is not writing a letter. For all x_16, x_16 will write a letter if and only if x_16 will drive a car. Can we infer the following from them? If we can, name the inference rule being used: For all x_16, x_16 is an electrician.
 From the fact that for all x_16, x_16 will write a letter if and only if x_16 will drive a car we can infer that for all x_16, if x_16 drives a car, then x_16 is writing a letter via universal biconditional elimination. From the fact that for all x_16, if x_16 drives a car, then x_16 is writing a letter, and that for all x_16, x_16 will drive a car we can infer that for all x_16, x_16 will write a letter via universal modus ponens. From the fact that there is at least one x_16 for which if x_16 were sad, then x_16 is not writing a letter, and that for all x_16, x_16 will write a letter we can infer that there is at least one x_16 for which x_16 is not sad via existential modus tollens. Finally, from the fact that for all x_16, if x_16 were an electrician, then x_16 is sad, and that there is at least one x_16 for which x_16 is not sad we can infer that there is at least one x_16 for which x_16 is not an electrician via existential modus tollens, which contradicts that For all x_16, x_16 is an electrician. Therefore, the answer is no.