Consider the following premises. s -> u. s <-> q_9. u -> q_9. Can we infer ~(u <-> s) from them? If possible, name the inference rules being used at each step.
 From s <-> q_9 we can infer q_9 -> s via biconditional elimination. From u -> q_9, q_9 -> s we can infer u -> s via transitivity. Finally, from u -> s, s -> u we can infer u <-> s via biconditional introduction, which contradicts ~(u <-> s). Therefore, the answer is no.