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Eigenfunctions of distinct eigenvalues with the same winding number are never parallel

Proved
FiniteEnergyPlane.loopEigen_apply_ne_smul_of_hasLoopEigenWind

by Mazecto · Nov 1, 2026 · Mathlib 0df444a (Lean v4.33.1)

conley-zehnder-indexpseudoholomorphic-curvessymplectic-geometrywinding-numbers

Let S∞:R→R2×2S_\infty:\mathbb{R}\to\mathbb{R}^{2\times2}S∞​:R→R2×2 be a C∞C^\inftyC∞ 111-periodic loop of symmetric matrices and A=−J0∂t−S∞A=-J_0\partial_t-S_\inftyA=−J0​∂t​−S∞​ on 111-periodic loops in R2\mathbb{R}^2R2. Let μ1≠μ2\mu_1\ne\mu_2μ1​=μ2​ be eigenvalues of AAA such that every eigenfunction of μ1\mu_1μ1​ and every eigenfunction of μ2\mu_2μ2​ has the same winding number k∈Zk\in\mathbb{Z}k∈Z. If e1,e2e_1,e_2e1​,e2​ are eigenfunctions with eigenvalues μ1,μ2\mu_1,\mu_2μ1​,μ2​, then for every t∈Rt\in\mathbb{R}t∈R and every c∈Rc\in\mathbb{R}c∈R,

e2(t)≠c e1(t).e_2(t)\ne c\,e_1(t).e2​(t)=ce1​(t).

The values of such eigenfunctions are linearly independent in R2\mathbb{R}^2R2 at every time. This controls how eigenfunctions of one winding number can combine.

Formalization Note Eigenfunctions are IsLoopEigen Sinf μ e (FiniteEnergyPlane_Asymptotics); the winding hypothesis on μj\mu_jμj​ is HasLoopEigenWind Sinf μⱼ k (FiniteEnergyPlane_Winding: μj\mu_jμj​ has an eigenfunction and all its eigenfunctions have winding kkk as loops in C\mathbb{C}C via vecToC); IsSymLoop Sinf and smoothness of the entries are hypotheses.

Preamble
import Definitions.Def_FiniteEnergyPlane_Winding
Formal statement
namespace FiniteEnergyPlane

open scoped ContDiff

/-- Eigenfunctions of `A = -J₀ ∂ₜ - S∞` for two distinct eigenvalues with the same winding
number are pointwise linearly independent: their values are never parallel. -/
theorem loopEigen_apply_ne_smul_of_hasLoopEigenWind (Sinf : ℝ → CauchyRiemannIndex.Mat 1)
    (hSinf : CauchyRiemannIndex.IsSymLoop Sinf)
    (hSinf' : ∀ i j, ContDiff ℝ ∞ (fun t => Sinf t i j)) {μ₁ μ₂ : ℝ} {k : ℤ} (hμ : μ₁ ≠ μ₂)
    (h₁ : HasLoopEigenWind Sinf μ₁ k) (h₂ : HasLoopEigenWind Sinf μ₂ k)
    {e₁ e₂ : ℝ → CauchyRiemannIndex.Vec 1} (he₁ : IsLoopEigen Sinf μ₁ e₁)
    (he₂ : IsLoopEigen Sinf μ₂ e₂) (t c : ℝ) : e₂ t ≠ c • e₁ t := by
  sorry

end FiniteEnergyPlane
Source
C. Wendl, Lectures on Symplectic Field Theory (2026 notes), arXiv:1612.01009, Section 3.7, Theorem 3.7.1; H. Hofer, K. Wysocki, E. Zehnder, GAFA 5 (1995), Section 3.

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