Consider the following premises. w -> u. s_1 -> r. u -> s_1. s_1 -> u. Can we infer w -> r from them?
 From u -> s_1, s_1 -> u we can infer u <-> s_1. From u <-> s_1 we can infer u -> s_1. From u -> s_1, s_1 -> r we can infer u -> r. Finally, from w -> u, u -> r we can infer w -> r. Therefore, the answer is yes.