Consider the following premises. q_2. q_2 -> u_2. ~q. s -> q. Can we infer ~u_2 from them? If possible, name the inference rules being used at each step.
 From s -> q, ~q we can infer ~s via modus tollens. Finally, from q_2 -> u_2, q_2 we can infer u_2 via modus ponens, which contradicts ~u_2. Therefore, the answer is no.