Consider the following premises. ~u_3 -> w_2. ~u_2. w_2 -> t. u_3 -> u_2. Can we infer ~t from them? If possible, name the inference rules being used at each step.
 From u_3 -> u_2, ~u_2 we can infer ~u_3 via modus tollens. From ~u_3 -> w_2, ~u_3 we can infer w_2 via modus ponens. Finally, from w_2 -> t, w_2 we can infer t via modus ponens, which contradicts ~t. Therefore, the answer is no.