Consider the following premises. t <-> w. u_4 <-> w. u_4 -> u. ~u. Can we infer t from them?
 From u_4 -> u, ~u we can infer ~u_4. From u_4 <-> w, ~u_4 we can infer ~w. Finally, from t <-> w, ~w we can infer ~t, which contradicts t. Therefore, the answer is no.