Consider the following premises. Joseph is writing a letter if and only if it is cold. It is cold if and only if Linda is taking a plane. For all z_4, z_4 will not take a plane. Can we infer the following from them? If we can, name the inference rule being used: Joseph is not writing a letter.
 From the fact that for all z_4, z_4 will not take a plane we can infer that Linda is not taking a plane via universal instantiation. From the fact that it is cold if and only if Linda is taking a plane, and that Linda is not taking a plane we can infer that it is not cold via biconditional elimination. Finally, from the fact that Joseph is writing a letter if and only if it is cold, and that it is not cold we can infer that Joseph is not writing a letter via biconditional elimination. Therefore, the answer is yes.