Consider the following premises. For all z_2, if z_2 works, then z_2 is taking a plane. There is at least one z_2 for which if z_2 takes a plane, then z_2 is a politician. For all z_2, if z_2 were a politician, then z_2 is an office clerk. For all z_2, if z_2 were an office clerk, then z_2 is working. Can we infer the following from them? There is at least one z_2 for which z_2 will work if and only if z_2 is a politician.
 From the fact that for all z_2, if z_2 works, then z_2 is taking a plane, and that there is at least one z_2 for which if z_2 takes a plane, then z_2 is a politician we can infer that there is at least one z_2 for which if z_2 works, then z_2 is a politician. From the fact that for all z_2, if z_2 were a politician, then z_2 is an office clerk, and that for all z_2, if z_2 were an office clerk, then z_2 is working we can infer that for all z_2, if z_2 were a politician, then z_2 is working. Finally, from the fact that there is at least one z_2 for which if z_2 works, then z_2 is a politician, and that for all z_2, if z_2 were a politician, then z_2 is working we can infer that there is at least one z_2 for which z_2 will work if and only if z_2 is a politician. Therefore, the answer is yes.