Consider the following premises. s -> q_3. q_3 -> u_2. ~u_2. u_2 -> s. Can we infer s from them?
 From s -> q_3, q_3 -> u_2 we can infer s -> u_2. From s -> u_2, u_2 -> s we can infer s <-> u_2. Finally, from s <-> u_2, ~u_2 we can infer ~s, which contradicts s. Therefore, the answer is no.