Consider the following premises. For all x, x is curious if and only if x is a janitor. For all x, if x were curious, then x is a janitor. For all x, x is not curious. Can we infer the following from them? There is at least one x for which x is a janitor.
 From the fact that for all x, x is curious if and only if x is a janitor we can infer that for all x, if x were a janitor, then x is curious. From the fact that for all x, if x were a janitor, then x is curious, and that for all x, if x were curious, then x is a janitor we can infer that for all x, x is a janitor if and only if x is curious. Finally, from the fact that for all x, x is a janitor if and only if x is curious, and that for all x, x is not curious we can infer that for all x, x is not a janitor, which contradicts that There is at least one x for which x is a janitor. Therefore, the answer is no.