Consider the following premises. t -> q_8. ~q_8. q_8 -> t. s -> t. t -> s. Can we infer ~s from them? If possible, name the inference rules being used at each step.
 From t -> q_8, q_8 -> t we can infer t <-> q_8 via biconditional introduction. From s -> t, t -> s we can infer s <-> t via biconditional introduction. From t <-> q_8, ~q_8 we can infer ~t via biconditional elimination. Finally, from s <-> t, ~t we can infer ~s via biconditional elimination. Therefore, the answer is yes.