Consider the following premises. forall x_20: P_20(x_20). s -> u. s. Can we infer u from them?
 From forall x_20: P_20(x_20) we can infer P_20(a_20). From s, P_20(a_20) we can infer s and P_20(a_20). From s and P_20(a_20) we can infer s. Finally, from s -> u, s we can infer u. Therefore, the answer is yes.