If B

C,+ 1 C, - 2C,C,+ 2 + C,+1 C,+ 2 ~ 0. But according to (6.3-13) of Lemma 6.3c, this result holds for r = 0,1, 2, · ··. Hence (6.3-18) is valid, as is (6.3-17), which proves the theorem. 0