Consider the following premises. u_3 -> r. p_7 <-> p_2. ~r. ~p_7. Can we infer p_2 from them? If possible, name the inference rules being used at each step.
 From u_3 -> r, ~r we can infer ~u_3 via modus tollens. Finally, from p_7 <-> p_2, ~p_7 we can infer ~p_2 via biconditional elimination, which contradicts p_2. Therefore, the answer is no.