Consider the following premises. r_1 or ~t. t or ~r_1. ~r_1. Can we infer ~t from them?
 From r_1 or ~t we can infer t -> r_1. From t or ~r_1 we can infer r_1 -> t. From t -> r_1, r_1 -> t we can infer t <-> r_1. Finally, from t <-> r_1, ~r_1 we can infer ~t. Therefore, the answer is yes.