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