Consider the following premises. There is at least one y_4 for which if y_4 were a bartender, then y_4 is a server. For all y_4, y_4 will write a letter or y_4 is a bartender. For all y_4, if y_4 writes a letter, then y_4 is a server. For all y_4, y_4 is a server if and only if y_4 will write a letter. Can we infer the following from them? There is at least one y_4 for which y_4 is a server.
 From the fact that for all y_4, y_4 is a server if and only if y_4 will write a letter we can infer that for all y_4, if y_4 were a server, then y_4 is writing a letter. From the fact that for all y_4, if y_4 were a server, then y_4 is writing a letter, and that for all y_4, if y_4 writes a letter, then y_4 is a server we can infer that for all y_4, y_4 is a server if and only if y_4 will write a letter. From the fact that for all y_4, y_4 is a server if and only if y_4 will write a letter we can infer that for all y_4, if y_4 writes a letter, then y_4 is a server. Finally, from the fact that for all y_4, if y_4 writes a letter, then y_4 is a server, that there is at least one y_4 for which if y_4 were a bartender, then y_4 is a server, and that for all y_4, y_4 will write a letter or y_4 is a bartender we can infer that there is at least one y_4 for which y_4 is a server. Therefore, the answer is yes.