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Universal real measurability transfers to finite-dimensional Euclidean spaces
Statement
In , every subset of is Lebesgue measurable for each positive finite .
Facts & Assumptions
Given: and in .
Every set of reals in the Solovay model is Lebesgue measurable: every subset of is measurable.
Dyadic coding supplies coin measure and its completed Lebesgue transfer: nonterminating binary codes identify interval measure with fair-coin cylinder measure.
The Euclidean Lebesgue measure is the completion of the product of the factor Lebesgue measures: -dimensional measure completes product measure.
The Solovay inner model satisfies Dependent Choice: satisfies DC.
AC implies DC implies countable choice: in ZF, DC implies countable choice, which supplies the precise choice hypothesis of F3.
Lebesgue outer measure, Lebesgue measurability and Lebesgue measure are unchanged by translation: translations preserve Lebesgue measurability in every finite dimension.
Proof
Let consist of the reals whose canonical binary code has no eventually- subsequence in any residue class modulo ; its complement is the finite union of Borel null sets. Split the digits of a code in by residue modulo . This is a Borel bijection with Borel inverse given by interleaving the canonical coordinate codes. A length- cylinder maps to the corresponding product of dyadic intervals, each of length ; both sides have measure . The monotone-class extension and F2–F3 make measure preserving on all Borel sets and send Borel null sets both ways. F3 assumes countable choice, supplied here exactly by internal DC through F4–F5; the digit map itself makes no selections.
For arbitrary , F1 makes measurable. Completion gives Borel and Borel null with . Put and , so both lie in the domain of . Bimeasurability and step 1.1 give , with Borel measurable and null ; hence is measurable.
Cover by the explicitly indexed disjoint half-open cubes , . For each , the set belongs to and is measurable by step 2.1; F6 makes its translate measurable. The defining closure of the Lebesgue sigma-algebra under the displayed countable union now gives measurable, with no selection of representatives. When , there is one residue class, for canonical non-eventually- codes, and is the identity under that code, so step 2.1 is exactly F1. The case is outside the stated positive range.
Depends on
- Every set of reals in the Solovay model is Lebesgue measurable
- The Solovay inner model satisfies Dependent Choice
- AC implies DC implies countable choice
- Dyadic coding supplies coin measure and its completed Lebesgue transfer
- The Euclidean Lebesgue measure is the completion of the product of the factor Lebesgue measures
- Lebesgue outer measure, Lebesgue measurability and Lebesgue measure are unchanged by translation
Used by
Dependency tree · two levels
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Sources
- Solovay 1970, Part III §4 (standard reference, not scraped)