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: forall x_21: P_21(x_21) -> W_2(x_21). forall x_21: W_2(x_21) <-> P(x_21). forall x_21: Q_21(x_21) -> W_2(x_21). forall x_21: P_21(x_21) or Q_21(x_21).
forall x_21: W_2(x_21) can be inferred via the universal disjunction elimination rule. forall x_21: W_2(x_21) -> P(x_21) can be inferred via the universal biconditional elimination rule. forall x_21: P(x_21) -> W_2(x_21) can be inferred via the universal biconditional elimination rule.