Consider the following premises. David is an artist. For all x_9, x_9 is a doctor if and only if x_9 is an artist. Can we infer the following from them? David is not a doctor.
 From the fact that for all x_9, x_9 is a doctor if and only if x_9 is an artist we can infer that for all x_9, if x_9 were an artist, then x_9 is a doctor. From the fact that for all x_9, if x_9 were an artist, then x_9 is a doctor we can infer that if David were an artist, then David is a doctor. Finally, from the fact that if David were an artist, then David is a doctor, and that David is an artist we can infer that David is a doctor, which contradicts that David is not a doctor. Therefore, the answer is no.