Consider the following premises. t -> u. q_13 -> u. u -> w_3. w_3 -> t. t. Can we infer ~u from them?
 From t we can infer t or q_13. From u -> w_3, w_3 -> t we can infer u -> t. From u -> t, t -> u we can infer u <-> t. From u <-> t we can infer t -> u. Finally, from t -> u, q_13 -> u, t or q_13 we can infer u, which contradicts ~u. Therefore, the answer is no.