Consider the following premises. ~r_3. t -> r_3. r_3 -> t. Can we infer ~t from them? If possible, name the inference rules being used at each step.
 From t -> r_3, r_3 -> t we can infer t <-> r_3 via biconditional introduction. Finally, from t <-> r_3, ~r_3 we can infer ~t via biconditional elimination. Therefore, the answer is yes.