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_1. w <-> t. w -> s_1. s <-> t.
~w can be inferred via the modus tollens rule. w -> t can be inferred via the biconditional elimination rule. s -> t can be inferred via the biconditional elimination rule. t -> w can be inferred via the biconditional elimination rule. t -> s can be inferred via the biconditional elimination rule.