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 <-> t. t <-> u. w or u.
w -> t can be inferred via the biconditional elimination rule. t -> u can be inferred via the biconditional elimination rule. t -> w can be inferred via the biconditional elimination rule. u -> t can be inferred via the biconditional elimination rule.