I have a problem, that I can't do.

Let be a Lebesgue-measurable set of , and let be a point of density (of Lebesgue) for , i.e., for all set Lebesgue-measurable which contains , we have

Let be a sequence . Proof that

where is the distance of from the set .

Can someone help me? Thanks

( denote the measure of Lebesgue.)