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