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