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One-parameter family of fast planes transverse to translations

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FiniteEnergyPlane.exists_fastPlane_slice_family

by Mazecto · Nov 6, 2026 · Mathlib 0df444a (Lean v4.33.1)

finite-energy-planespseudoholomorphic-curvessymplectic-geometry

Let S=H−1(1)⊂V1=R4S = H^{-1}(1) \subset V_1 = \mathbb{R}^4S=H−1(1)⊂V1​=R4 be a strictly star-shaped level with a compatible complex structure JJJ on ξ\xiξ, and let PPP be a periodic Reeb orbit on SSS whose Conley–Zehnder index is at least 333. Let uuu be an embedded fast finite-energy plane asymptotic to PPP at ∞\infty∞. Then for every l≥1l \ge 1l≥1 there are r>0r > 0r>0 and a ClC^lCl map g:C×(−r,r)→V1g : \mathbb{C} \times (-r, r) \to V_1g:C×(−r,r)→V1​ such that:

  1. g(⋅,0)=ug(\cdot, 0) = ug(⋅,0)=u;
  2. every g(⋅,t)g(\cdot, t)g(⋅,t), ∣t∣<r|t| < r∣t∣<r, is a fast finite-energy plane asymptotic to PPP at ∞\infty∞;
  3. the map (z,c,t)↦c⋅g(z,t)=e2cg(z,t)(z, c, t) \mapsto c \cdot g(z, t) = e^{2c} g(z, t)(z,c,t)↦c⋅g(z,t)=e2cg(z,t) is injective on C×(−r,r)×(−r,r)\mathbb{C} \times (-r, r) \times (-r, r)C×(−r,r)×(−r,r);
  4. this map has injective derivative everywhere: if Dg(z,t)(Δ,δt)+λ g(z,t)=0Dg(z, t)(\Delta, \delta t) + \lambda\, g(z, t) = 0Dg(z,t)(Δ,δt)+λg(z,t)=0 with Δ∈C\Delta \in \mathbb{C}Δ∈C and δt,λ∈R\delta t, \lambda \in \mathbb{R}δt,λ∈R, then Δ=0\Delta = 0Δ=0, δt=0\delta t = 0δt=0 and λ=0\lambda = 0λ=0.

Thus the planes g(⋅,t)g(\cdot, t)g(⋅,t) form a one-parameter family through uuu that is transverse to the R\mathbb{R}R-translations in the symplectization, and the small translates of its members are pairwise disjoint. This is the geometric content of Hryniewicz, Fast finite-energy planes in symplectizations and applications, Trans. AMS 364 (2012), Lemmas 6.10 and 6.20, written in a form where the R\mathbb{R}R-translation parameter is explicit.

Formalization Note: V1∖{0}V_1 \setminus \{0\}V1​∖{0} is the model of the symplectization R×S\mathbb{R} \times SR×S, in which the translation by ccc is y↦e2cyy \mapsto e^{2c} yy↦e2cy. Item 4 is the injectivity of the derivative of the map in item 3 at (z,c,t)(z, c, t)(z,c,t), after dividing by e2ce^{2c}e2c and writing λ=2 δc\lambda = 2\,\delta cλ=2δc. Since the map ggg is only asserted to be ClC^lCl on the open set C×(−r,r)\mathbb{C} \times (-r, r)C×(−r,r), no uniformity as ∣z∣→∞|z| \to \infty∣z∣→∞ is part of the statement. Non-vacuity: for the round sphere with J=iJ = iJ=i, g(z,t)=(z,eit)g(z, t) = (z, e^{it})g(z,t)=(z,eit) satisfies the conclusion for u(z)=(z,1)u(z) = (z, 1)u(z)=(z,1).

Preamble
import Definitions.Def_FiniteEnergyPlane_Fredholm
Formal statement
namespace FiniteEnergyPlane

open MeasureTheory Metric Filter Topology
open scoped ContDiff ENNReal Real

/-- A one-parameter family of fast planes through an embedded fast plane, transverse to the
`ℝ`-translations. Let `u` be an embedded fast finite-energy plane asymptotic to `P` at `∞`, where
the Conley–Zehnder index of `P` is at least `3`. Then for every `l ≥ 1` there are `r > 0` and a
`C^l` map `g : ℂ × (-r, r) → V 1` with `g(·, 0) = u` such that every `g(·, t)` is a fast
finite-energy plane asymptotic to `P` at `∞`, and such that
`(z, c, t) ↦ c · g(z, t) = e^{2c} • g(z, t)` is injective on `ℂ × (-r, r) × (-r, r)` with injective
derivative. The latter is stated at `c = 0`: `D g(z, t)(Δ, δt) + λ • g(z, t) = 0` forces
`Δ = 0`, `δt = 0` and `λ = 0`. -/
theorem exists_fastPlane_slice_family (H : V 1 → ℝ) (hH : IsStrictlyStarShapedLevel H)
    (J : V 1 → V 1 →L[ℝ] V 1) (hJ : IsCompatibleXiStructure H J)
    (P : ReebOrbit H) (hcz : P.IsCZAtLeast 3) (u : ℂ → V 1)
    (hu : IsFastPlane H J u) (huP : IsNondegenerateEnd H u cylInf P 1)
    (hue : IsEmbeddedPlane u) (l : ℕ) (hl : 1 ≤ l) :
    ∃ r > 0, ∃ g : ℂ × ℝ → V 1, ContDiffOn ℝ l g (Set.univ ×ˢ Set.Ioo (-r) r) ∧
      (∀ z, g (z, 0) = u z) ∧
      (∀ t ∈ Set.Ioo (-r) r, IsFastPlane H J (fun z => g (z, t)) ∧
        IsNondegenerateEnd H (fun z => g (z, t)) cylInf P 1) ∧
      Set.InjOn (fun q : ℂ × ℝ × ℝ => Real.exp (2 * q.2.1) • g (q.1, q.2.2))
        (Set.univ ×ˢ (Set.Ioo (-r) r ×ˢ Set.Ioo (-r) r)) ∧
      ∀ z, ∀ t ∈ Set.Ioo (-r) r, ∀ (Δ : ℂ) (δt lam : ℝ),
        fderiv ℝ g (z, t) (Δ, δt) + lam • g (z, t) = 0 → Δ = 0 ∧ δt = 0 ∧ lam = 0 := by
  sorry

end FiniteEnergyPlane
Source
U. Hryniewicz, Fast finite-energy planes in symplectizations and applications, Trans. AMS 364 (2012), Lemmas 6.10 and 6.20, Theorem 2.3; H. Hofer, K. Wysocki, E. Zehnder, Properties of pseudoholomorphic curves in symplectisations III: Fredholm theory, Birkhäuser (1999)

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