Consider the following premises. w_4 or ~s_4. s_4 or ~w_4. Can we infer ~(w_4 -> s_4) from them?
 From w_4 or ~s_4 we can infer s_4 -> w_4. Finally, from s_4 or ~w_4 we can infer w_4 -> s_4, which contradicts ~(w_4 -> s_4). Therefore, the answer is no.