To proceed further, we need the following lemma.
Lemma: If satisfies (2.5) and then
Proof of the Lemma: The first inequality of (2.6) follows by induction. It is trivially true for . Assuming that is true for we have from (2.5)
![](Images/image069.png)
Hence (2.6) is true for , and thus for all ![](Images/image073.png)
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