Consider the following premises. ~u_1. ~u. u or q_4. u_1 <-> t_2. Can we infer t_2 from them?
 From u_1 <-> t_2 we can infer t_2 -> u_1. Finally, from t_2 -> u_1, ~u_1 we can infer ~t_2, which contradicts t_2. Therefore, the answer is no.