Consider the following premises. p_9 <-> t. t or ~p_9. Can we infer ~(t <-> p_9) from them? If possible, name the inference rules being used at each step.
 From p_9 <-> t we can infer t -> p_9 via biconditional elimination. From t or ~p_9 we can infer p_9 -> t via rewriting. Finally, from t -> p_9, p_9 -> t we can infer t <-> p_9 via biconditional introduction, which contradicts ~(t <-> p_9). Therefore, the answer is no.