In the proof of Proposition 2 (see discussion following relation), Lemma 6 is used for n =

Question:

In the proof of Proposition 2 (see discussion following relation), Lemma 6 is used for n = 1 to ensure finiteness of ɛX2, which, according to the lemma, follows from the existence and finiteness of f(2)(0). Prove this fact directly; i.e., show that the existence and finiteness of f(2)(0) implies finiteness of ɛX2.