Consider the following premises. For all x_7, x_7 is a politician or x_7 is an artist. For all x_7, x_7 is not a cashier. For all x_7, x_7 is a cashier if and only if x_7 is a politician. Can we infer the following from them? David is not an artist.
 From the fact that for all x_7, x_7 is a cashier if and only if x_7 is a politician, and that for all x_7, x_7 is not a cashier we can infer that for all x_7, x_7 is not a politician. Finally, from the fact that for all x_7, x_7 is a politician or x_7 is an artist, and that for all x_7, x_7 is not a politician we can infer that for all x_7, x_7 is an artist, which contradicts that David is not an artist. Therefore, the answer is no.