Consider the following premises. q_1 -> u. u -> r. r_1 -> q_1. r -> q_4. Can we infer ~(r_1 -> q_4) from them?
 From u -> r, r -> q_4 we can infer u -> q_4. From r_1 -> q_1, q_1 -> u we can infer r_1 -> u. Finally, from r_1 -> u, u -> q_4 we can infer r_1 -> q_4, which contradicts ~(r_1 -> q_4). Therefore, the answer is no.