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