Consider the following premises. u_3 or ~q. u_3 or ~p. p or q. Can we infer ~u_3 from them?
 From u_3 or ~p we can infer p -> u_3. From u_3 or ~q we can infer q -> u_3. Finally, from p -> u_3, q -> u_3, p or q we can infer u_3, which contradicts ~u_3. Therefore, the answer is no.