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