Consider the following premises. u or u_3. u_3 <-> t. u -> w. w -> t. Can we infer ~t from them? If possible, name the inference rules being used at each step.
 From u -> w, w -> t we can infer u -> t via transitivity. From u_3 <-> t we can infer u_3 -> t via biconditional elimination. Finally, from u -> t, u_3 -> t, u or u_3 we can infer t via disjunction elimination, which contradicts ~t. Therefore, the answer is no.