Consider the following premises. s or w. ~w or u_4. ~s. Can we infer p_4 or u_4 from them? If possible, name the inference rules being used at each step.
 From s or w, ~s we can infer w via disjunctive syllogism. From w we can infer w or p_4 via addition. Finally, from w or p_4, ~w or u_4 we can infer p_4 or u_4 via resolution. Therefore, the answer is yes.