Consider the following premises. ~r. t_4 -> s. s -> t_4. t_4 -> r. Can we infer s from them?
 From s -> t_4, t_4 -> s we can infer s <-> t_4. From t_4 -> r, ~r we can infer ~t_4. Finally, from s <-> t_4, ~t_4 we can infer ~s, which contradicts s. Therefore, the answer is no.