Consider the following premises. For all x_9, if x_9 works, then x_9 is sleeping. There is at least one x_9 for which if x_9 works, then x_9 is not a musician. For all x_9, x_9 is a musician. For all x_9, if x_9 sleeps, then x_9 is working. Can we infer the following from them? If we can, name the inference rule being used: For all x_9, x_9 will sleep.
 From the fact that for all x_9, if x_9 sleeps, then x_9 is working, and that for all x_9, if x_9 works, then x_9 is sleeping we can infer that for all x_9, x_9 will sleep if and only if x_9 will work via universal biconditional introduction. From the fact that there is at least one x_9 for which if x_9 works, then x_9 is not a musician, and that for all x_9, x_9 is a musician we can infer that there is at least one x_9 for which x_9 will not work via existential modus tollens. Finally, from the fact that for all x_9, x_9 will sleep if and only if x_9 will work, and that there is at least one x_9 for which x_9 will not work we can infer that there is at least one x_9 for which x_9 will not sleep via existential biconditional elimination, which contradicts that For all x_9, x_9 will sleep. Therefore, the answer is no.