Consider the following premises. q_6 or q. q -> u. q_6 -> u. u -> q_6. Can we infer ~u from them?
 From u -> q_6, q_6 -> u we can infer u <-> q_6. From u <-> q_6 we can infer q_6 -> u. Finally, from q_6 -> u, q -> u, q_6 or q we can infer u, which contradicts ~u. Therefore, the answer is no.