Consider the following premises. For all x_11, x_11 will work. For all x_10, if x_10 works, then x_10 is a police officer. For all x_10, if x_10 were a police officer, then x_10 is working. Can we infer the following from them? If we can, name the inference rule being used: David is a police officer.
 From the fact that for all x_11, x_11 will work we can infer that David is working via universal instantiation. From the fact that for all x_10, if x_10 works, then x_10 is a police officer, and that for all x_10, if x_10 were a police officer, then x_10 is working we can infer that for all x_10, x_10 will work if and only if x_10 is a police officer via universal biconditional introduction. From the fact that for all x_10, x_10 will work if and only if x_10 is a police officer we can infer that for all x_10, if x_10 works, then x_10 is a police officer via universal biconditional elimination. From the fact that for all x_10, if x_10 works, then x_10 is a police officer we can infer that if David works, then David is a police officer via universal instantiation. Finally, from the fact that if David works, then David is a police officer, and that David is working we can infer that David is a police officer via modus ponens. Therefore, the answer is yes.