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: s -> p_15. w_2 -> s. p_15 <-> w_2. w_2 -> s.
w_2 -> p_15 can be inferred via the transitivity rule. w_2 -> p_15 can be inferred via the transitivity rule. p_15 -> w_2 can be inferred via the biconditional elimination rule. w_2 -> p_15 can be inferred via the biconditional elimination rule.