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