Consider the following premises. For all x_7, if x_7 were a soldier, then x_7 is a writer. For all x_7, x_7 will drive a car or x_7 is sad. For all x_7, if x_7 were sad, then x_7 is a soldier. For all x_7, x_7 will drive a car if and only if x_7 is a writer. Can we infer the following from them? If we can, name the inference rule being used: For all x_7, x_7 is a writer.
 From the fact that for all x_7, x_7 will drive a car if and only if x_7 is a writer we can infer that for all x_7, if x_7 drives a car, then x_7 is a writer via universal biconditional elimination. From the fact that for all x_7, if x_7 were sad, then x_7 is a soldier, and that for all x_7, if x_7 were a soldier, then x_7 is a writer we can infer that for all x_7, if x_7 were sad, then x_7 is a writer via universal transitivity. Finally, from the fact that for all x_7, if x_7 drives a car, then x_7 is a writer, that for all x_7, if x_7 were sad, then x_7 is a writer, and that for all x_7, x_7 will drive a car or x_7 is sad we can infer that for all x_7, x_7 is a writer via universal disjunction elimination. Therefore, the answer is yes.