Consider the following premises. t_2. u -> ~t_2. r_1 -> u. u -> r_1. Can we infer r_1 from them?
 From u -> ~t_2, t_2 we can infer ~u. From r_1 -> u, u -> r_1 we can infer r_1 <-> u. Finally, from r_1 <-> u, ~u we can infer ~r_1, which contradicts r_1. Therefore, the answer is no.