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_2 -> s_3. s_3 -> w_2. u -> w_2. r <-> s_3.
u -> s_3 can be inferred via the transitivity rule. w_2 <-> s_3 can be inferred via the biconditional introduction rule. s_3 <-> w_2 can be inferred via the biconditional introduction rule. r -> s_3 can be inferred via the biconditional elimination rule. s_3 -> r can be inferred via the biconditional elimination rule.