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C-infinity convergence of a periodic map evaluated along a convergent family

Proved
FiniteEnergyPlane.tendstoZeroCInfty_comp_periodic

by Mazecto · Oct 30, 2026 · Mathlib 0df444a (Lean v4.33.1)

asymptotic-analysisdifferential-calculusreal-analysis

Let EEE be a finite-dimensional real normed space, FFF a real normed space, T,r>0T,r>0T,r>0, a,b∈Ra,b\in\mathbb{R}a,b∈R, and let Φ:R×E→F\Phi:\mathbb{R}\times E\to FΦ:R×E→F be C∞C^\inftyC∞ on R×B(0,r)\mathbb{R}\times B(0,r)R×B(0,r), TTT-periodic in its first variable there, with Φ(φ,0)=0\Phi(\varphi,0)=0Φ(φ,0)=0. If v:R2→Ev:\mathbb{R}^2\to Ev:R2→E satisfies v(s,t)→0v(s,t)\to0v(s,t)→0 in C∞C^\inftyC∞, uniformly in ttt, as s→+∞s\to+\inftys→+∞, then also

Φ(at+b, v(s,t))→0in C∞, uniformly in t.\Phi\big(at+b,\,v(s,t)\big)\to0\quad\text{in }C^\infty,\text{ uniformly in }t.Φ(at+b,v(s,t))→0in C∞, uniformly in t.

This carries C∞C^\inftyC∞ convergence through coordinates built along a periodic orbit, such as tube coordinates near a Reeb orbit.

Formalization Note C∞C^\inftyC∞ convergence is TendstoZeroCInfty (smooth on some (s0,∞)×R(s_0,\infty)\times\mathbb{R}(s0​,∞)×R, every derivative tends to 000 uniformly in ttt). EEE is a finite-dimensional real normed space and FFF any real normed space; Φ\PhiΦ is only assumed smooth and periodic on R×B(0,r)\mathbb{R}\times B(0,r)R×B(0,r).

Preamble
import Definitions.Def_FiniteEnergyPlane_Asymptotics
Formal statement
namespace FiniteEnergyPlane

open Metric
open scoped ContDiff

/-- Let `Φ(φ, v)` be smooth on `ℝ × B(0, r)`, `T`-periodic in `φ`, with `Φ(φ, 0) = 0`. If
`v(s, t) → 0` in `C^∞` on the end, then so does `Φ(a t + b, v(s, t))`, for any `a, b ∈ ℝ`. -/
theorem tendstoZeroCInfty_comp_periodic {E F : Type*} [NormedAddCommGroup E] [NormedSpace ℝ E]
    [FiniteDimensional ℝ E] [NormedAddCommGroup F] [NormedSpace ℝ F]
    (Φ : ℝ × E → F) (T r a b : ℝ) (hT : 0 < T) (hr : 0 < r)
    (hΦ : ContDiffOn ℝ ∞ Φ (Set.univ ×ˢ ball (0 : E) r))
    (hper : ∀ (φ : ℝ) (v : E), ‖v‖ < r → Φ (φ + T, v) = Φ (φ, v))
    (h0 : ∀ φ : ℝ, Φ (φ, 0) = 0)
    (v : ℝ × ℝ → E) (hv : TendstoZeroCInfty v) :
    TendstoZeroCInfty (fun p : ℝ × ℝ => Φ (a * p.2 + b, v p)) := by
  sorry

end FiniteEnergyPlane
Source
Used for U. Hryniewicz, J. Symplectic Geom. 12 (2014), arXiv:1105.2077, Theorems 2.10-2.11, and H. Hofer, K. Wysocki, E. Zehnder, Properties of pseudoholomorphic curves in symplectisations I: asymptotics, Ann. Inst. H. Poincaré Anal. Non Linéaire 13 (1996)

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