Consider the following premises. There is at least one z_4 for which z_4 is a mechanic if and only if z_4 is a lawyer. For all z_4, if z_4 were a lawyer, then z_4 is a janitor. For all z_4, z_4 is a mechanic. Can we infer the following from them? There is at least one z_4 for which z_4 is a janitor.
 From the fact that there is at least one z_4 for which z_4 is a mechanic if and only if z_4 is a lawyer we can infer that there is at least one z_4 for which if z_4 were a mechanic, then z_4 is a lawyer. From the fact that there is at least one z_4 for which if z_4 were a mechanic, then z_4 is a lawyer, and that for all z_4, if z_4 were a lawyer, then z_4 is a janitor we can infer that there is at least one z_4 for which if z_4 were a mechanic, then z_4 is a janitor. Finally, from the fact that there is at least one z_4 for which if z_4 were a mechanic, then z_4 is a janitor, and that for all z_4, z_4 is a mechanic we can infer that there is at least one z_4 for which z_4 is a janitor. Therefore, the answer is yes.