Consider the following premises. p_6 or ~r_2. p_6 -> q_6. q_6 -> r_2. Can we infer ~(r_2 <-> p_6) from them?
 From p_6 -> q_6, q_6 -> r_2 we can infer p_6 -> r_2. From p_6 or ~r_2 we can infer r_2 -> p_6. Finally, from r_2 -> p_6, p_6 -> r_2 we can infer r_2 <-> p_6, which contradicts ~(r_2 <-> p_6). Therefore, the answer is no.