Consider the following premises. If David works, then Sarah is playing tennis. For all x_15, x_15 is rich. For all x_14, if x_14 were rich, then x_14 is working. Can we infer the following from them? If we can, name the inference rule being used: Sarah is not playing tennis.
 From the fact that for all x_15, x_15 is rich we can infer that David is rich via universal instantiation. From the fact that for all x_14, if x_14 were rich, then x_14 is working we can infer that if David were rich, then David is working via universal instantiation. From the fact that if David were rich, then David is working, and that David is rich we can infer that David is working via modus ponens. Finally, from the fact that if David works, then Sarah is playing tennis, and that David is working we can infer that Sarah is playing tennis via modus ponens, which contradicts that Sarah is not playing tennis. Therefore, the answer is no.