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The Solovay inner model satisfies ZF and every real set has a real–ordinal definition
Statement
is a transitive ZF inner model with the same ordinals and reals as . Every in is definable in from a real and finitely many ordinals, equivalently from one countable ordinal sequence.
Facts & Assumptions
Given: The supplied Solovay extension.
The hereditarily ordinal-sequence-definable Solovay model: defines by hereditary -ordinal definability.
The Lévy collapse localizes countable ordinal data: localizes every member of and every real.
Absorption, factorization, and homogeneous truth in the Solovay collapse: homogeneous tail truth is independent of its generic.
The inaccessible Lévy-collapse setup for Solovay's construction: the forcing ground is .
Proof
Hereditary definability makes transitive, contains every ordinal, and contains every real because a real is itself an -parameter; Extensionality, Foundation, Pairing, Union and Infinity are therefore inherited.
Separation is obtained by conjoining the defining formula of the separated class with the fixed definitions of its set parameters. For Replacement, if and is functional on , the ambient set is defined from the fixed hereditary codes of and by ; every such is already in the transitive class , so the image is hereditarily and belongs to . No per-value codes are selected or combined. For Power Set, the ambient set is defined from by the uniform predicate, and all members of its transitive closure lie in . Thus every ZF axiom holds in .
Let lie in . Heredity gives a definition of from and finitely many ordinals . By F2, lies in a bounded initial extension. The real-capture clause of F3 supplies a real and ordinal such that is definable over from . By F4, . The class is uniformly definable in from , so syntactically restricting every quantifier in the fixed defining formula to defines the same unique in . Substitute that ambient definition of into the definition of . Thus is definable in from and the finite ordinal tuple . Conversely, interleave the natural-number bits of and the finite tuple into one countable ordinal sequence in . Hence the advertised parameter forms are equivalent, without claiming that an arbitrary ordinal is real-coded or that .
Depends on
Used by
- Solovay's model proves that an inaccessible cardinal exists False statement
- Fixed finite-fragment verification for the Solovay construction Lemma
- The Solovay inner model is closed under ambient omega-sequences Lemma
- Every set of reals in the Solovay model has the Baire property Theorem
- Every set of reals in the Solovay model is Lebesgue measurable Theorem
- Every uncountable Solovay-model set of reals has a perfect subset Theorem
Dependency tree · two levels
19 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
- Solovay 1970, Part III, Lemmas 2.4 and 2.8 (standard reference, not scraped)