Consider the following premises. p_12 -> q. p_12 <-> u. s_2 -> q. s_2. Can we infer ~q from them?
 From p_12 <-> u we can infer u -> p_12. From u -> p_12, p_12 -> q we can infer u -> q. From s_2 we can infer s_2 or u. Finally, from s_2 -> q, u -> q, s_2 or u we can infer q, which contradicts ~q. Therefore, the answer is no.