Consider the following premises. p_6 -> t. t -> t_2. t_2 <-> t_4. Can we infer p_6 -> t_4 from them?
 From p_6 -> t, t -> t_2 we can infer p_6 -> t_2. From t_2 <-> t_4 we can infer t_2 -> t_4. Finally, from p_6 -> t_2, t_2 -> t_4 we can infer p_6 -> t_4. Therefore, the answer is yes.