Consider the following premises. w or r_2. s_2 or ~r_2. w -> s_2. s -> ~s_2. Can we infer ~s from them?
 From s_2 or ~r_2 we can infer r_2 -> s_2. From w -> s_2, r_2 -> s_2, w or r_2 we can infer s_2. Finally, from s -> ~s_2, s_2 we can infer ~s. Therefore, the answer is yes.