Consider the following premises. p_6 -> t. p_6 or ~r_11. t -> q. q -> r_11. Can we infer ~(r_11 <-> p_6) from them?
 From t -> q, q -> r_11 we can infer t -> r_11. From p_6 -> t, t -> r_11 we can infer p_6 -> r_11. From p_6 or ~r_11 we can infer r_11 -> p_6. Finally, from r_11 -> p_6, p_6 -> r_11 we can infer r_11 <-> p_6, which contradicts ~(r_11 <-> p_6). Therefore, the answer is no.