Consider the following premises. ~q or r_2. r_2 -> u. q or p_1. p_1 -> u. Can we infer u from them?
 From q or p_1, ~q or r_2 we can infer p_1 or r_2. Finally, from p_1 -> u, r_2 -> u, p_1 or r_2 we can infer u. Therefore, the answer is yes.