Consider the following premises. q_2 or ~u. p and w. ~q_2. Can we infer u from them? If possible, name the inference rules being used at each step.
 From q_2 or ~u we can infer u -> q_2 via rewriting. Finally, from u -> q_2, ~q_2 we can infer ~u via modus tollens, which contradicts u. Therefore, the answer is no.