Consider the following premises. If Robert were a doctor, then it is snowing. Robert is a doctor if and only if it is snowing. Can we infer the following from them? If we can, name the inference rule being used: It is snowing if and only if Robert is a doctor.
 From the fact that Robert is a doctor if and only if it is snowing we can infer that if it snows, then Robert is a doctor via biconditional elimination. Finally, from the fact that if it snows, then Robert is a doctor, and that if Robert were a doctor, then it is snowing we can infer that it is snowing if and only if Robert is a doctor via biconditional introduction. Therefore, the answer is yes.