Consider the following premises. p_9 or ~u_2. p_9 -> u_2. u_2. Can we infer ~p_9 from them? If possible, name the inference rules being used at each step.
 From p_9 or ~u_2 we can infer u_2 -> p_9 via rewriting. From p_9 -> u_2, u_2 -> p_9 we can infer p_9 <-> u_2 via biconditional introduction. From p_9 <-> u_2 we can infer u_2 -> p_9 via biconditional elimination. Finally, from u_2 -> p_9, u_2 we can infer p_9 via modus ponens, which contradicts ~p_9. Therefore, the answer is no.