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TheoremStatement: Literature-sourcedProof: AI-adaptedPipeline-generatedjudge pass (gpt-5.6-terra)audited 2026-09-14
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Every limit ordinal has cofinality omega in Gitik's model

Statement

In NG, every nonzero limit ordinal λ has a cofinal map ωλ. Consequently NGcf(λ)=ω for every such λ.

Facts & Assumptions

Given: The completed Gitik symmetric model NG.

[F1]

Gitik's symmetric submodel satisfies ZF: NG is a transitive ZF model containing the ground model.

[F2]

Gitik's filter system and proper-class forcing: At every regular coordinate δ, trunks have finite one-to-one δ-sections, support extension is available, and successors are selected from uniform filters on δ.

[F3]

Gitik's finite-support symmetric submodel: A name fixed by the pointwise stabilizer of one coordinate and having HS subnames belongs to NG.

Proof

1.1

Fix an infinite regular ground cardinal δ. Use the canonical name whose value is the union of the δ-sections of conditions in G: a pair n,ξ enters the named graph exactly under conditions with p(δ)(n)=ξ. Directedness makes this union a one-to-one partial map. For every n<ω, support extension and finitely many legal successors give a dense class of conditions whose δ-section contains n. For every ξ<δ, uniformity makes each relevant successor set unbounded, so pruning above ξ and taking the next δ-successor is dense. Thus the value gδ:ωδ is total and cofinal, but need not be onto. Every automorphism in H{δ} fixes the δ-section and permutes the witnessing conditions only outside that coordinate. Its graph entries use only check names, so the name is hereditarily symmetric with support {δ}. F3 therefore puts gδ in NG.

F2F3
2.1

Let λ be a nonzero limit ordinal. In the ground model put δ=cfM(λ) and take the strictly increasing cofinal map h:δλ supplied by F4. Its check name is fixed by every automorphism and hereditarily symmetric, so F3 puts h in NG. If δ=ω, it is already the required witness. If δ>ω, then δ is an infinite regular ground cardinal, so step 1.1 gives gδNG and ZF in F1 forms c=hgδ:ωλ. Given ξ<λ, choose η<δ with ξh(η) and then n<ω with ηgδ(n). Monotonicity of h gives ξc(n), so c is cofinal. This proves the claimed omega upper bound in both cases without any surjectivity assertion.

F1F2F3F4step 1.1
3.1

By F4, the cofinality of a limit ordinal is infinite. Equivalently, the empty range is not cofinal and every nonempty finite set of ordinals has a maximum still below λ, so no finite map is cofinal in λ. Step 2.1 gives a cofinal map of length ω; since ω is the least infinite ordinal, the least cofinal length is exactly ω. The construction and this verification take place inside the transitive ZF model NG.

F1F4step 2.1

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