Consider the following premises. ~p_23. u -> p. p_23 <-> p. ~u <-> t_2. Can we infer t_2 from them? If possible, name the inference rules being used at each step.
 From p_23 <-> p we can infer p -> p_23 via biconditional elimination. From u -> p, p -> p_23 we can infer u -> p_23 via transitivity. From u -> p_23, ~p_23 we can infer ~u via modus tollens. From ~u <-> t_2 we can infer ~u -> t_2 via biconditional elimination. Finally, from ~u -> t_2, ~u we can infer t_2 via modus ponens. Therefore, the answer is yes.