Consider the following premises. s_4 -> s. p_11 <-> s. p_11 -> s_4. Can we infer ~(p_11 -> s) from them?
 From p_11 <-> s we can infer s -> p_11. Finally, from p_11 -> s_4, s_4 -> s we can infer p_11 -> s, which contradicts ~(p_11 -> s). Therefore, the answer is no.