Consider the following premises. ~q_19. t_1 <-> q_19. p_3 <-> q_9. ~p_3. Can we infer ~q_9 from them? If possible, name the inference rules being used at each step.
 From t_1 <-> q_19, ~q_19 we can infer ~t_1 via biconditional elimination. Finally, from p_3 <-> q_9, ~p_3 we can infer ~q_9 via biconditional elimination. Therefore, the answer is yes.