Consider the following premises. It is sunny if and only if Thomas is taking a plane. For all y_1, y_1 will not take a plane. It is sunny 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 not cold.
 From the fact that for all y_1, y_1 will not take a plane we can infer that Thomas is not taking a plane via universal instantiation. From the fact that it is sunny if and only if Thomas is taking a plane, and that Thomas is not taking a plane we can infer that it is not sunny via biconditional elimination. Finally, from the fact that it is sunny if and only if it is cold, and that it is not sunny we can infer that it is not cold via biconditional elimination. Therefore, the answer is yes.