Consider the following premises. t or ~p_7. p_7 or ~t. Can we infer ~(p_7 <-> t) from them? If possible, name the inference rules being used at each step.
 From p_7 or ~t we can infer t -> p_7 via rewriting. From t or ~p_7 we can infer p_7 -> t via rewriting. Finally, from p_7 -> t, t -> p_7 we can infer p_7 <-> t via biconditional introduction, which contradicts ~(p_7 <-> t). Therefore, the answer is no.