What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Name the inference rule being used: u or ~q_9. u <-> q_9.
q_9 -> u can be inferred via the rewriting rule. u -> q_9 can be inferred via the biconditional elimination rule. q_9 -> u can be inferred via the biconditional elimination rule.