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: ~w_1. w_1 -> t. t -> w_1.
~t can be inferred via the modus tollens rule. w_1 <-> t can be inferred via the biconditional introduction rule. t <-> w_1 can be inferred via the biconditional introduction rule.