Consider the following premises. ~u. u_4 -> ~q_15. u. u_4 <-> t. Can we infer ~t from them?
 From u we can infer u or q_15. From u or q_15, ~u we can infer q_15. From u_4 -> ~q_15, q_15 we can infer ~u_4. Finally, from u_4 <-> t, ~u_4 we can infer ~t. Therefore, the answer is yes. Notice, however, that the premises were contradictory, so we can infer anything from them.