Consider the following premises. r -> t. r -> t. ~t. t -> r. Can we infer ~r from them?
 From t -> r, r -> t we can infer t <-> r. From t <-> r we can infer t -> r. From r -> t, t -> r we can infer r <-> t. Finally, from r <-> t, ~t we can infer ~r. Therefore, the answer is yes.