Consider the following premises. u_2 -> t. ~t. p -> u_2. Can we infer p from them? If possible, name the inference rules being used at each step.
 From u_2 -> t, ~t we can infer ~u_2 via modus tollens. Finally, from p -> u_2, ~u_2 we can infer ~p via modus tollens, which contradicts p. Therefore, the answer is no.