Consider the following premises. r -> u_4. p_8 <-> p. q_20. p -> ~q_20. r. Can we infer p_8 from them?
 From p -> ~q_20, q_20 we can infer ~p. From r -> u_4, r we can infer u_4. Finally, from p_8 <-> p, ~p we can infer ~p_8, which contradicts p_8. Therefore, the answer is no.