Consider the following premises. r_4 -> t. r_4. t -> r_4. Can we infer ~t from them? If possible, name the inference rules being used at each step.
 From t -> r_4, r_4 -> t we can infer t <-> r_4 via biconditional introduction. From t <-> r_4 we can infer r_4 -> t via biconditional elimination. Finally, from r_4 -> t, r_4 we can infer t via modus ponens, which contradicts ~t. Therefore, the answer is no.