Very difficult Real Analysis question on Lebesgue integration

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SUMMARY

The discussion centers on a challenging Real Analysis problem involving Lebesgue integration, specifically proving the integrability of a limit function g given a sequence of nonnegative, integrable functions gn converging almost everywhere. The key condition is that for every ε > 0, there exists a δ > 0 such that for any measurable set A with measure less than δ, the supremum of the integrals of gn over A is less than ε. The conclusion drawn is that g is integrable and that the integral of g over [0, 1] equals the limit of the integrals of gn as n approaches infinity.

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  • Lebesgue integration theory
  • Convergence theorems in measure theory
  • Understanding of measurable functions
  • Knowledge of supremum and limit concepts
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  • Study the Dominated Convergence Theorem in Lebesgue integration
  • Explore the Monotone Convergence Theorem and its applications
  • Learn about the properties of measurable functions and their integrability
  • Investigate the interchange of limit and integral in Lebesgue integration
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Students and professionals in mathematics, particularly those focusing on Real Analysis, measure theory, and Lebesgue integration, will find this discussion beneficial for deepening their understanding of integrability and convergence concepts.

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Suppose gn are nonnegative and integrable on [0, 1], and that gn [tex]\rightarrow[/tex] g almost everywhere.

Further suppose that for all [tex]\epsilon[/tex] > 0, [tex]\exists[/tex] [tex]\delta[/tex] > 0 such that for all A [tex]\subset[/tex] [0, 1], we have

meas(A) < [tex]\delta[/tex] implies that supn [tex]\int[/tex]A |gn| < [tex]\epsilon[/tex].

Prove that g is integrable, and that [tex]\int[/tex][0,1] g = lim [tex]\int[/tex][0,1] gn.

Attempt at the solution:
There are some observations I've compiled. First, for an set A with measure less than [tex]\delta[/tex], we know that the the limiting function g exists on that set. So, it's integral is also bounded by the sup. But from here, I don't know how to argue that the limiting function has a uniform bound on all of [0, 1].
 
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Have you tried any of the well-known theorems in Lebesgue integration regarding interchange of limit and integral?
 

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