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: t <-> q_9. p_4 <-> q_9.
t -> q_9 can be inferred via the biconditional elimination rule. p_4 -> q_9 can be inferred via the biconditional elimination rule. q_9 -> t can be inferred via the biconditional elimination rule. q_9 -> p_4 can be inferred via the biconditional elimination rule.