Consider the following premises. ~t_3. r <-> t. r <-> t_3. Can we infer ~t from them? If possible, name the inference rules being used at each step.
 From r <-> t_3 we can infer r -> t_3 via biconditional elimination. From r -> t_3, ~t_3 we can infer ~r via modus tollens. Finally, from r <-> t, ~r we can infer ~t via biconditional elimination. Therefore, the answer is yes.