Consider the following premises. p_2 or ~s_4. p_2 -> r. Can we infer ~(s_4 -> r) from them?
 From p_2 or ~s_4 we can infer s_4 -> p_2. Finally, from s_4 -> p_2, p_2 -> r we can infer s_4 -> r, which contradicts ~(s_4 -> r). Therefore, the answer is no.