Consider the following premises. If Charles were not a musician, then Charles is poor. It is snowing if and only if Charles is a musician. It is not snowing. Can we infer the following from them? If we can, name the inference rule being used: Charles is poor or David is an office clerk.
 From the fact that it is snowing if and only if Charles is a musician, and that it is not snowing we can infer that Charles is not a musician via biconditional elimination. From the fact that if Charles were not a musician, then Charles is poor, and that Charles is not a musician we can infer that Charles is poor via modus ponens. Finally, from the fact that Charles is poor we can infer that Charles is poor or David is an office clerk via addition. Therefore, the answer is yes.