Consider the following premises. ~p_13. p_13 or w. r_2 -> ~w. Can we infer ~r_2 or u from them?
 From p_13 or w, ~p_13 we can infer w. From r_2 -> ~w, w we can infer ~r_2. Finally, from ~r_2 we can infer ~r_2 or u. Therefore, the answer is yes.