Consider the following premises. w_2 -> u. s <-> w_2. w_2 or ~u. ~u. Can we infer ~s from them?
 From w_2 or ~u we can infer u -> w_2. From w_2 -> u, u -> w_2 we can infer w_2 <-> u. From w_2 <-> u, ~u we can infer ~w_2. Finally, from s <-> w_2, ~w_2 we can infer ~s. Therefore, the answer is yes.