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_2. s -> t. s <-> t_2. t -> s.
s <-> t can be inferred via the biconditional introduction rule. t <-> s can be inferred via the biconditional introduction rule. s -> t_2 can be inferred via the biconditional elimination rule. t_2 -> s can be inferred via the biconditional elimination rule. ~s can be inferred via the biconditional elimination rule.