Consider the following premises. q -> t. p_9 -> q. p_9 <-> t. Can we infer t <-> q from them?
 From p_9 <-> t we can infer t -> p_9. From t -> p_9, p_9 -> q we can infer t -> q. Finally, from t -> q, q -> t we can infer t <-> q. Therefore, the answer is yes.