Consider the following premises. For all x_11, x_11 will read a book. If William were fast, then Charles is an office clerk. For all x_11, x_11 is an office clerk if and only if x_11 is a janitor. For all x_11, if x_11 were a janitor, then x_11 is not reading a book. Can we infer the following from them? If we can, name the inference rule being used: William is not fast.
 From the fact that for all x_11, if x_11 were a janitor, then x_11 is not reading a book, and that for all x_11, x_11 will read a book we can infer that for all x_11, x_11 is not a janitor via universal modus tollens. From the fact that for all x_11, x_11 is an office clerk if and only if x_11 is a janitor, and that for all x_11, x_11 is not a janitor we can infer that for all x_11, x_11 is not an office clerk via universal biconditional elimination. From the fact that for all x_11, x_11 is not an office clerk we can infer that Charles is not an office clerk via universal instantiation. Finally, from the fact that if William were fast, then Charles is an office clerk, and that Charles is not an office clerk we can infer that William is not fast via modus tollens. Therefore, the answer is yes.