<p>Stationary logic is the extension of first-order logic with a quantifier expressing that “almost all” countable subsets of a structure have a given property. This paper studies <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(C(aa)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>C</mi> <mo stretchy="false">(</mo> <mi>a</mi> <mi>a</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>, the smallest model of ZF containing the ordinal numbers and closed under the satisfaction predicate for stationary logic. This model was constructed by Kennedy et al. (2024) as a generalization of Gödel’s constructible universe <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(L\)</EquationSource> <EquationSource Format="MATHML"><math> <mi>L</mi> </math></EquationSource> </InlineEquation>, obtained by iterating definability in stationary logic rather than first-order logic. Unlike <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(L\)</EquationSource> <EquationSource Format="MATHML"><math> <mi>L</mi> </math></EquationSource> </InlineEquation>, however, <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(C(aa)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>C</mi> <mo stretchy="false">(</mo> <mi>a</mi> <mi>a</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> can contain large cardinals far beyond a measurable cardinal. We show in this paper that nevertheless, assuming large cardinals in <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(V\)</EquationSource> <EquationSource Format="MATHML"><math> <mi>V</mi> </math></EquationSource> </InlineEquation>, the inner model <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(C(aa)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>C</mi> <mo stretchy="false">(</mo> <mi>a</mi> <mi>a</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> shares many of the nice properties of <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(L\)</EquationSource> <EquationSource Format="MATHML"><math> <mi>L</mi> </math></EquationSource> </InlineEquation>. In particular, we prove that <InlineEquation ID="IEq11"> <EquationSource Format="TEX">\(C(aa)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>C</mi> <mo stretchy="false">(</mo> <mi>a</mi> <mi>a</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> satisfies the Generalized Continuum Hypothesis, the Ultrapower Axiom, and the axiom <InlineEquation ID="IEq12"> <EquationSource Format="TEX">\(V = \text {HOD}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>V</mi> <mo>=</mo> <mtext>HOD</mtext> </mrow> </math></EquationSource> </InlineEquation>.</p>

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The structure of \(C(aa)\)

  • Gabriel Goldberg,
  • John Steel

摘要

Stationary logic is the extension of first-order logic with a quantifier expressing that “almost all” countable subsets of a structure have a given property. This paper studies \(C(aa)\) C ( a a ) , the smallest model of ZF containing the ordinal numbers and closed under the satisfaction predicate for stationary logic. This model was constructed by Kennedy et al. (2024) as a generalization of Gödel’s constructible universe \(L\) L , obtained by iterating definability in stationary logic rather than first-order logic. Unlike \(L\) L , however, \(C(aa)\) C ( a a ) can contain large cardinals far beyond a measurable cardinal. We show in this paper that nevertheless, assuming large cardinals in \(V\) V , the inner model \(C(aa)\) C ( a a ) shares many of the nice properties of \(L\) L . In particular, we prove that \(C(aa)\) C ( a a ) satisfies the Generalized Continuum Hypothesis, the Ultrapower Axiom, and the axiom \(V = \text {HOD}\) V = HOD .