Consider the following premises. p_2 -> u_2. u_2 -> ~t. t. Can we infer ~p_2 or t_4 from them? If possible, name the inference rules being used at each step.
 From u_2 -> ~t, t we can infer ~u_2 via modus tollens. From p_2 -> u_2, ~u_2 we can infer ~p_2 via modus tollens. Finally, from ~p_2 we can infer ~p_2 or t_4 via addition. Therefore, the answer is yes.