Consider the following premises. ~s_4. u_2. u_2 -> s_4. Can we infer u or t_4 from them?
 From u_2 -> s_4, ~s_4 we can infer ~u_2. From ~u_2 we can infer ~u_2 or u. From ~u_2 or u, u_2 we can infer u. Finally, from u we can infer u or t_4. Therefore, the answer is yes. Notice, however, that the premises were contradictory, so we can infer anything from them.