Consider the following premises. q_2 <-> q_8. u -> q_2. t -> q_8. u or t. Can we infer ~q_8 from them?
 From q_2 <-> q_8 we can infer q_2 -> q_8. From u -> q_2, q_2 -> q_8 we can infer u -> q_8. Finally, from u -> q_8, t -> q_8, u or t we can infer q_8, which contradicts ~q_8. Therefore, the answer is no.