Consider the following premises. There is at least one z_2 for which z_2 will drink water if and only if z_2 is a bartender. For all z_2, z_2 is a musician if and only if z_2 will drink water. Can we infer the following from them? There is at least one z_2 for which if z_2 were a musician, then z_2 is a bartender.
 From the fact that there is at least one z_2 for which z_2 will drink water if and only if z_2 is a bartender we can infer that there is at least one z_2 for which if z_2 drinks water, then z_2 is a bartender. From the fact that for all z_2, z_2 is a musician if and only if z_2 will drink water we can infer that for all z_2, if z_2 were a musician, then z_2 is drinking water. Finally, from the fact that for all z_2, if z_2 were a musician, then z_2 is drinking water, and that there is at least one z_2 for which if z_2 drinks water, then z_2 is a bartender we can infer that there is at least one z_2 for which if z_2 were a musician, then z_2 is a bartender. Therefore, the answer is yes.