Consider the following premises. q_6 -> t_3. t_3 -> q_6. ~q. t_3 -> q. Can we infer q_6 from them? If possible, name the inference rules being used at each step.
 From t_3 -> q_6, q_6 -> t_3 we can infer t_3 <-> q_6 via biconditional introduction. From t_3 -> q, ~q we can infer ~t_3 via modus tollens. Finally, from t_3 <-> q_6, ~t_3 we can infer ~q_6 via biconditional elimination, which contradicts q_6. Therefore, the answer is no.