Consider the following premises. ~p_9 or r_9. p_9 or p. ~u_2. u_2 -> p. p -> u_2. Can we infer ~r_9 from them? If possible, name the inference rules being used at each step.
 From p_9 or p, ~p_9 or r_9 we can infer p or r_9 via resolution. From u_2 -> p, p -> u_2 we can infer u_2 <-> p via biconditional introduction. From u_2 <-> p, ~u_2 we can infer ~p via biconditional elimination. Finally, from p or r_9, ~p we can infer r_9 via disjunctive syllogism, which contradicts ~r_9. Therefore, the answer is no.