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