We have that X A 1 and X A 2 are 2-combinable, and their merge is the new position set X = X A 1 ∪ X A 2 = {1, 2, 3}.
in case r b < r(p), we are not guaranteed to have achieved an optimal reduction in the rank, but we can still obtain an asymptotic improvement in parsing time if we use the new productions obtained in the transformation.