Consider the following premises. t_1 -> r_1. u -> t_1. r_1 -> u. q_4 <-> u. ~q_4. Can we infer ~r_1 from them?
 From q_4 <-> u, ~q_4 we can infer ~u. From u -> t_1, t_1 -> r_1 we can infer u -> r_1. From u -> r_1, r_1 -> u we can infer u <-> r_1. Finally, from u <-> r_1, ~u we can infer ~r_1. Therefore, the answer is yes.