Consider the following premises. u -> r_6. p_1 -> u. r_1 -> r. r_1 or p_1. r -> r_6. Can we infer ~r_6 from them?
 From r_1 -> r, r -> r_6 we can infer r_1 -> r_6. From p_1 -> u, u -> r_6 we can infer p_1 -> r_6. Finally, from r_1 -> r_6, p_1 -> r_6, r_1 or p_1 we can infer r_6, which contradicts ~r_6. Therefore, the answer is no.