Consider the following premises. forall x_20: P_20(x_20). ~s. s or u_2. Can we infer u_2 from them? If possible, name the inference rules being used at each step.
 From forall x_20: P_20(x_20) we can infer P_20(h) via universal instantiation. Finally, from s or u_2, ~s we can infer u_2 via disjunctive syllogism. Therefore, the answer is yes.