Please solve the exercise 3.20.

Thank you.

Proposition 3.18. Il 11....S. E PLX,10), then it holds , 4 - 1, To prove this proposition, we need the next lemma. Lemma 3.19. Let / PLCX,...). Then there erists {}, such that OS 01 () S (1) S... 56;(1) S... 5 f(x) and lim (*) (*) are valid for all I EX Proofs of Proposition 3.18 and Lemma 3.19. The key point of the proof of Lemma 3.19 is to consider E* = {r X 1 (x)