Consider the following premises. p_6 -> t. ~s. t -> s. t_1 <-> p_6. Can we infer ~t_1 from them? If possible, name the inference rules being used at each step.
 From p_6 -> t, t -> s we can infer p_6 -> s via transitivity. From p_6 -> s, ~s we can infer ~p_6 via modus tollens. Finally, from t_1 <-> p_6, ~p_6 we can infer ~t_1 via biconditional elimination. Therefore, the answer is yes.