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Theorem 1.16(ii) — near-equal-mass rational global sections

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BirkhoffGlobalSection.near_equal_mass_birkhoff_rational_global_section

by Yivy Yu · Sep 12, 2026 · Mathlib 0df444a (Lean v4.33.1)

celestial-mechanicsdynamical-systemshamiltonian-dynamics

There exists 0<ε≤1/20<\varepsilon\leq1/20<ε≤1/2 such that, whenever

0<μ<1,∣μ−12∣<ε,−c<h1(μ),0<\mu<1, \qquad \left|\mu-\frac12\right|<\varepsilon, \qquad -c<h_1(\mu),0<μ<1,​μ−21​​<ε,−c<h1​(μ),

the complete antipodally equivariant Levi-Civita Hamiltonian flow on Σμ,c\Sigma_{\mu,c}Σμ,c​ has a geometric Birkhoff retrograde orbit whose prime image in the antipodal quotient binds a rational two-disk global surface of section.

This is an existential single-page consequence of Liu--Salomão Theorems 5.1 and 1.16(ii). Theorem 5.1 supplies a q2q_2q2​-symmetric geometric retrograde orbit at every subcritical energy; Theorem 1.16(ii) proves, for mass ratios sufficiently close to 1/21/21/2, that every retrograde orbit in either regularized component binds a rational open book whose pages are global surfaces of section. The paper works with elliptic--hyperbolic regularization and the associated Reeb flow. A proof of this Lean row must therefore also transport the result to the Levi-Civita antipodal quotient and verify preservation under the positive time change; that bridge is not silently treated as part of the cited theorem statement.

Preamble
import Definitions.Def_BirkhoffGlobalSection
Formal statement
namespace BirkhoffGlobalSection

/-- The existential single-page consequence of Liu--Salomão, Theorems 5.1 and
1.16(ii), transported to the Levi-Civita quotient model. A proof must include
the regularization and positive-time-change bridge between the two models. -/
theorem near_equal_mass_birkhoff_rational_global_section :
    ∃ ε : ℝ, 0 < ε ∧ ε ≤ 1 / 2 ∧
      ∀ μ c : ℝ, 0 < μ → μ < 1 →
        |μ - 1 / 2| < ε → belowFirstCriticalValue μ c →
        ∀ (φ : Flow ℝ (LeftEnergyState μ c)),
          IsLeviCivitaHamiltonianFlow μ c φ →
          ∀ hanti : IsAntipodallyEquivariantFlow μ c φ,
          ∃ δ : AntipodalPeriodicTrajectory φ,
            IsGeometricBirkhoffRetrogradeTrajectory φ δ ∧
              RationalDiskLikeGlobalSurfaceOfSection φ hanti
                (antipodalTrajectoryDoubleLift φ hanti δ) := by sorry

end BirkhoffGlobalSection
Source
Liu--Salomão, Theorems 5.1 and 1.16(ii), https://arxiv.org/abs/2506.17867v2. The Lean row also requires the model-transport and positive-time-change bridge from their elliptic--hyperbolic/Reeb formulation to the Levi-Civita antipodal quotient.
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What the Lean code literally says, in plain math · OpenAI Codex

Read-back model: OpenAI Codex. File SHA-256: 24fbdf7708e8cafcfb04d4e578840350bc7df7b1d9590e08a9a6ca6bbe57afe6. This declaration is an admitted by sorry goal, not a proved theorem. It asserts that there exists a real εεε with 0<ε≤1/20<ε≤1/20<ε≤1/2 such that, for every real μ,cμ,cμ,c satisfying 0<μ<10<μ<10<μ<1, ∣μ−1/2∣<ε|μ-1/2|<ε∣μ−1/2∣<ε, and −c<sInf⁡(Vμ)-c<\operatorname{sInf}(V_μ)−c<sInf(Vμ​), and for every real flow φφφ on the subtype XXX of the connected component of Kμ,c=0K_{μ,c}=0Kμ,c​=0 with positive second-collision distance based at (0,0,1−μ,0)(0,0,\sqrt{1-μ},0)(0,0,1−μ​,0), the following holds: if every ambient orbit curve has derivative XKX_KXK​ at time zero, then for every proof hhh that all existing antipodal state pairs evolve antipodally at every real time, there exists an AntipodalPeriodicTrajectory δδδ. Writing its point as xxx and period as PPP, this means P>0P>0P>0, φP(x)=−xφ_P(x)=-xφP​(x)=−x, and for every 0<t<P0<t<P0<t<P, φt(x)φ_t(x)φt​(x) is neither xxx nor −x-x−x. It is geometrically retrograde in the literal sense that zNormSq(φtx)>0zNormSq(φ_t x)>0zNormSq(φt​x)>0 for every real ttt, its Jacobi projection at −t-t−t is (q1,−q2,−p1,p2)(q_1,-q_2,-p_1,p_2)(q1​,−q2​,−p1​,p2​) of its projection at ttt, its chosen-primary relative-position curve is injective on [0,P)[0,P)[0,P), and that curve has global continuous polar functions with positive radius, radius period PPP, and angle gain 2π2π2π per PPP. Let γγγ be the constructed PeriodicOrbit with point xxx and period 2P2P2P. The conclusion also requires the following rational-page predicate for γγγ: the component is invariant under s↦−ss↦-ss↦−s and contains no s=−ss=-ss=−s; the quotient Q=X/(s∼s′  ⟺  s=s′ or s=−s′)Q=X/(s∼s'\iff s=s'\text{ or }s=-s')Q=X/(s∼s′⟺s=s′ or s=−s′) has jointly continuous descended time maps satisfying time-zero identity and time-addition composition; the quotient class of xxx returns at time PPP and at no 0<t<P0<t<P0<t<P; and there are a page p:R2→R4p:\mathbb R^2→\mathbb R^4p:R2→R4 and proof that its closed-unit-disk image lies in the component such that ppp is C∞C^∞C∞, injective, and immersive on the closed disk, XK(p(u))X_K(p(u))XK​(p(u)) is outside Dp(u)Dp(u)Dp(u) on the open disk, the upstairs boundary image is the full orbit set of γγγ, the induced quotient page is continuous, its open-disk restriction is a topological embedding, two closed-disk parameters have the same quotient image exactly when they are equal or are antipodal boundary points, the quotient boundary image equals the quotient orbit, and every quotient state outside that orbit hits the quotient open page at times larger than every prescribed real bound and smaller than every prescribed real bound. Here VμV_μVμ​ is the set of collision-free differentiable zero-derivative Jacobi critical values. The declaration does not assert existence of a qualifying flow or equivariance proof, any astronomical sign inequality, a first-return map, quotient smoothness, or identification of QQQ with a named manifold.

Human review
  • Endorsed by Shuze Chen · Sep 12, 2026

  • Endorsed by Yivy Yu · Sep 12, 2026

    Confirmed by the mission captain (proposal self-audit).

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