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