Consider the following premises. u_1 -> w_4. t -> s. s -> w_4. p_3. u_1 or t. Can we infer ~w_4 from them?
 From t -> s, s -> w_4 we can infer t -> w_4. Finally, from u_1 -> w_4, t -> w_4, u_1 or t we can infer w_4, which contradicts ~w_4. Therefore, the answer is no.