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_2. t <-> u_2. t or w.
w -> u_2 can be inferred via the biconditional elimination rule. t -> u_2 can be inferred via the biconditional elimination rule. u_2 -> w can be inferred via the biconditional elimination rule. u_2 -> t can be inferred via the biconditional elimination rule.