Consider the following premises. p_1 <-> t_2. ~u. t_2 -> u. Can we infer ~p_1 from them? If possible, name the inference rules being used at each step.
 From p_1 <-> t_2 we can infer p_1 -> t_2 via biconditional elimination. From p_1 -> t_2, t_2 -> u we can infer p_1 -> u via transitivity. Finally, from p_1 -> u, ~u we can infer ~p_1 via modus tollens. Therefore, the answer is yes.