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