How statement and proof provenance work
The first chip identifies the source of the statement or construction; the second identifies the source of its local proof or verification.
- Literature-sourced: the exact statement appears in a cited source; only wording and notation differ.
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These labels describe origin, not correctness: citations and verification chips remain separate evidence.
Assuming choice on the cosets of in , a Vitali set in exists
Statement
Assume the Axiom of Choice. Then there exists a Vitali set in the sense of Vitali set on .
Facts & Assumptions
Given: The Axiom of Choice.
A Vitali set on is a subset meeting every equivalence class of in exactly one point (Vitali set on ).
Every family of nonempty sets has a choice function (The Axiom of Choice).
A choice function for a family is a function with domain such that for every (Choice function).
Proof
Let be the family of all sets of the form with . Each member of is nonempty because it contains its defining point, and distinct members are exactly the equivalence classes of the relation in [F1].
By [A1] and [F2] there is a choice function on . Put . Then meets every member of , and it meets each of them in exactly one point because assigns one value to each set in its domain.
Since the members of are exactly the equivalence classes of on , step 2.1 says precisely that is a Vitali set on .
Remarks
- The proof uses one simultaneous selector on the family of -cosets meeting . Nothing in the proof reduces that family to a countable one.
Depends on
Used by
- Every subset of ℝ of positive Lebesgue outer measure contains a nonmeasurable subset Corollary
- A Vitali set shows that not every subset of ℝ is Lebesgue measurable Counterexample
- Two disjoint nonmeasurable subsets of [0,1] can have the measurable union [0,1] Counterexample
- FALSE: assuming the Axiom of Choice, every subset of ℝ is Lebesgue measurable False statement
- What the Vitali set, Bernstein sets and free ultrafilters cost in choice Remark
- Assuming the Axiom of Choice, no translation-invariant measure on P(ℝ) is both finite and nonzero on [0,1] Theorem
Dependency tree · two levels
8 results within two dependency steps of this one, each drawn at its shortest distance from it. An arrow runs from a result to what uses it, so the chart reads left to right and ends at this result, which carries a heavier outline. Every node is a link to that result. Click elsewhere on the chart to enlarge it.
Sources
- Jacek Cichoń, Aleksander Kharazishvili, and Bogdan Węglorz, Subsets of the Real Line, Chapter 8 (standard reference, not scraped)
- Vitali set (Wikipedia) (standard reference, not scraped)