Consider the following premises. ~p_5. t_2 -> u_2. p_5 <-> t_2. u_2 -> t_2. Can we infer u_2 from them? If possible, name the inference rules being used at each step.
 From p_5 <-> t_2, ~p_5 we can infer ~t_2 via biconditional elimination. From t_2 -> u_2, u_2 -> t_2 we can infer t_2 <-> u_2 via biconditional introduction. Finally, from t_2 <-> u_2, ~t_2 we can infer ~u_2 via biconditional elimination, which contradicts u_2. Therefore, the answer is no.