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