Consider the following premises. q_6 -> t. t -> q_6. t -> q_6. Can we infer ~(q_6 <-> t) from them? If possible, name the inference rules being used at each step.
 From t -> q_6, q_6 -> t we can infer t <-> q_6 via biconditional introduction. From t <-> q_6 we can infer q_6 -> t via biconditional elimination. Finally, from q_6 -> t, t -> q_6 we can infer q_6 <-> t via biconditional introduction, which contradicts ~(q_6 <-> t). Therefore, the answer is no.