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 -> t. p_9 <-> t. p_9 -> u.
p_9 -> t can be inferred via the transitivity rule. p_9 -> t can be inferred via the biconditional elimination rule. t -> p_9 can be inferred via the biconditional elimination rule.