Consider the following premises. t -> s. t or ~q_7. s -> q_7. Can we infer ~(q_7 <-> s) from them? If possible, name the inference rules being used at each step.
 From t or ~q_7 we can infer q_7 -> t via rewriting. From q_7 -> t, t -> s we can infer q_7 -> s via transitivity. Finally, from q_7 -> s, s -> q_7 we can infer q_7 <-> s via biconditional introduction, which contradicts ~(q_7 <-> s). Therefore, the answer is no.