Consider the following premises. For all x_15, if x_15 were fast, then x_15 is an artist. For all x_15, x_15 is not an artist. It is overcast if and only if Sarah is fast. Can we infer the following from them? If we can, name the inference rule being used: It is overcast.
 From the fact that for all x_15, if x_15 were fast, then x_15 is an artist, and that for all x_15, x_15 is not an artist we can infer that for all x_15, x_15 is not fast via universal modus tollens. From the fact that for all x_15, x_15 is not fast we can infer that Sarah is not fast via universal instantiation. Finally, from the fact that it is overcast if and only if Sarah is fast, and that Sarah is not fast we can infer that it is not overcast via biconditional elimination, which contradicts that It is overcast. Therefore, the answer is no.