Tuesday, 15 September 2015

lebesgue measure - Continuous function with derivative a.e. and Luzin N property is absolutely continuous



Let f:IR be a continuous function which derivative exists a.e. and f exists in I. Also, suppose f satisfies the Luzin N property. Show that f is absolutely continuous.



So I don't seem to find any way to tackle this problem. This seems to be covered everywhere when the derivative is defined everywhere, but no such case when it's only a.e.



What I know is that using bounded variation it's possible to get absolute continuity, however I can't find how to prove the bounded variation condition.



Is there a reference or a way to solve this problem?


Answer




See 2. here. The theorem that's being proven assumes bv, but that condition is only used to establish that f has a derivative a.e. that is integrable, which are exactly the conditions you have.


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