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: s <-> t. r_8 -> t. t -> q. ~r_8. q -> r_8.
~q can be inferred via the modus tollens rule. r_8 -> q can be inferred via the transitivity rule. t -> r_8 can be inferred via the transitivity rule. q -> t can be inferred via the transitivity rule. s -> t can be inferred via the biconditional elimination rule. t -> s can be inferred via the biconditional elimination rule.