Consider the following premises. t or ~r. r or ~t. t <-> u. ~u. Can we infer r from them?
 From t <-> u, ~u we can infer ~t. From r or ~t we can infer t -> r. From t or ~r we can infer r -> t. From r -> t, t -> r we can infer r <-> t. Finally, from r <-> t, ~t we can infer ~r, which contradicts r. Therefore, the answer is no.