Consider the following premises. There is at least one x_6 for which x_6 will not sleep. For all x_6, x_6 will sleep if and only if x_6 will read a book. For all x_6, x_6 will read a book if and only if x_6 is a janitor. Can we infer the following from them? There is at least one x_6 for which x_6 is not a janitor.
 From the fact that for all x_6, x_6 will sleep if and only if x_6 will read a book, and that there is at least one x_6 for which x_6 will not sleep we can infer that there is at least one x_6 for which x_6 will not read a book. Finally, from the fact that for all x_6, x_6 will read a book if and only if x_6 is a janitor, and that there is at least one x_6 for which x_6 will not read a book we can infer that there is at least one x_6 for which x_6 is not a janitor. Therefore, the answer is yes.