Consider the following premises. t_2 -> q_6. t_2 -> q_6. q_6 -> t_2. Can we infer q_6 <-> t_2 from them?
 From t_2 -> q_6, q_6 -> t_2 we can infer t_2 <-> q_6. From t_2 <-> q_6 we can infer q_6 -> t_2. Finally, from q_6 -> t_2, t_2 -> q_6 we can infer q_6 <-> t_2. Therefore, the answer is yes.