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: q -> p_9. u or w. p_9 <-> u. w -> q.
w -> p_9 can be inferred via the transitivity rule. p_9 -> u can be inferred via the biconditional elimination rule. u -> p_9 can be inferred via the biconditional elimination rule.