Showing that a particular G_delta set exists with a measure property

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SUMMARY

The discussion centers on the existence of a G_delta set with a measure property, specifically regarding the covering of a bounded set E by countable collections of nonempty open, bounded intervals. Participants highlight that the assumption of E being bounded allows for finite coverings, but the challenge lies in demonstrating that the intersection of these covers forms a G_delta set. The necessity of controlling the measure of the covers is emphasized, indicating that the bounded nature of E is crucial for establishing the required properties of the set.

PREREQUISITES
  • Understanding of G_delta sets in topology
  • Knowledge of measure theory and outer measure
  • Familiarity with open and bounded intervals in real analysis
  • Concept of countable collections in set theory
NEXT STEPS
  • Research the properties of G_delta sets in relation to measure theory
  • Study the concept of outer measure and its implications for bounded sets
  • Explore techniques for constructing covers of sets in real analysis
  • Learn about the intersection properties of countable families of sets
USEFUL FOR

Mathematicians, particularly those specializing in topology and measure theory, as well as students seeking to deepen their understanding of G_delta sets and their measure properties.

jdinatale
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Ok, I don't think I'm on the right track here. I ASSUMED that the set of all countable collections [itex]\{I_k\}_{k = 1}^\infty[/itex] of nonempty open, bounded intervals such that [itex]E \subseteq \bigcup_{k = 1}^\infty I_k[/itex] is a countable set itself, which it probably isn't.

I'm not even sure where to start on this problem. I feel like I need to use the assumption that E is bounded. I know if E is bounded, then E can be covered by a finite number of nonempty open, bounded intervals.
 
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jdinatale said:
png_zps63374024.png

Ok, I don't think I'm on the right track here. I ASSUMED that the set of all countable collections [itex]\{I_k\}_{k = 1}^\infty[/itex] of nonempty open, bounded intervals such that [itex]E \subseteq \bigcup_{k = 1}^\infty I_k[/itex] is a countable set itself, which it probably isn't.

It's not. If you had a countable family of covers of this type, could you show that their intersection was a [itex]G_\delta[/itex] set? Presumably that's the direction that you were going with this part of the argument. Then you'd at least have a [itex]G_\delta[/itex] cover, and all that is left is to rig it so that it has the correct measure.

I'm not even sure where to start on this problem. I feel like I need to use the assumption that E is bounded. I know if E is bounded, then E can be covered by a finite number of nonempty open, bounded intervals.

You have a decent start. You just don't have any control (measure-wise) over your covers. You need to use the assumption that [itex]E[/itex] is bounded to get that control. If [itex]E[/itex] is bounded, what can you say about its outer measure?
 

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