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) -> R_21(x_21). forall x_21: Q_21(x_21) -> R_21(x_21). forall x_21: R_21(x_21) <-> Q_16(x_21). forall x_21: P_21(x_21) or Q_21(x_21).
forall x_21: R_21(x_21) can be inferred via the universal disjunction elimination rule. forall x_21: R_21(x_21) -> Q_16(x_21) can be inferred via the universal biconditional elimination rule. forall x_21: Q_16(x_21) -> R_21(x_21) can be inferred via the universal biconditional elimination rule.