Consider the following premises. If Charles works, then David is a doctor. Charles is working or David is not a doctor. David is not a doctor. Can we infer the following from them? If we can, name the inference rule being used: Charles is working.
 From the fact that Charles is working or David is not a doctor we can infer that if David were a doctor, then Charles is working via rewriting. From the fact that if Charles works, then David is a doctor, and that if David were a doctor, then Charles is working we can infer that Charles is working if and only if David is a doctor via biconditional introduction. Finally, from the fact that Charles is working if and only if David is a doctor, and that David is not a doctor we can infer that Charles is not working via biconditional elimination, which contradicts that Charles is working. Therefore, the answer is no.