Consider the following premises. There is at least one x_6 for which x_6 is a server if and only if x_6 is a taxi driver. For all x_6, x_6 is not a taxi driver. For all x_6, if x_6 were a taxi driver, then x_6 is a server. Can we infer the following from them? There is at least one x_6 for which x_6 is not a server.
 From the fact that there is at least one x_6 for which x_6 is a server if and only if x_6 is a taxi driver we can infer that there is at least one x_6 for which if x_6 were a server, then x_6 is a taxi driver. From the fact that for all x_6, if x_6 were a taxi driver, then x_6 is a server, and that there is at least one x_6 for which if x_6 were a server, then x_6 is a taxi driver we can infer that there is at least one x_6 for which x_6 is a taxi driver if and only if x_6 is a server. Finally, from the fact that there is at least one x_6 for which x_6 is a taxi driver if and only if x_6 is a server, and that for all x_6, x_6 is not a taxi driver we can infer that there is at least one x_6 for which x_6 is not a server. Therefore, the answer is yes.