Consider the following premises. It is sunny or Richard is not taking a plane. If it is sunny, then Richard is taking a plane. Richard is not taking a plane. Can we infer the following from them? If we can, name the inference rule being used: It is not sunny.
 From the fact that it is sunny or Richard is not taking a plane we can infer that if Richard takes a plane, then it is sunny via rewriting. From the fact that if it is sunny, then Richard is taking a plane, and that if Richard takes a plane, then it is sunny we can infer that it is sunny if and only if Richard is taking a plane via biconditional introduction. Finally, from the fact that it is sunny if and only if Richard is taking a plane, and that Richard is not taking a plane we can infer that it is not sunny via biconditional elimination. Therefore, the answer is yes.