Consider the following premises. Jennifer is a server if and only if it is late. For all z_2, z_2 is not a server. Can we infer the following from them? It is late.
 From the fact that for all z_2, z_2 is not a server we can infer that Jennifer is not a server. Finally, from the fact that Jennifer is a server if and only if it is late, and that Jennifer is not a server we can infer that it is not late, which contradicts that It is late. Therefore, the answer is no.