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A Cauchy estimate for an exponential polynomial that vanishes on a grid

Proved
Transcendence.expPoly_grid_estimate

by carlok · Sep 27, 2026 · Mathlib 0df444a (Lean v4.33.1)

complex-analysisdiaz-modulus-leanexponential-polynomialstranscendence

Let y1,…,yl∈Cy_1, \dots, y_l \in \mathbb{C}y1​,…,yl​∈C be linearly independent over Q\mathbb{Q}Q, and let F(z)=∑k∈sckzekeωkzF(z) = \sum_{k \in s} c_k z^{e_k} e^{\omega_k z}F(z)=∑k∈s​ck​zek​eωk​z with ∣ωk∣≤W|\omega_k| \le W∣ωk​∣≤W and ek≤Ee_k \le Eek​≤E for all kkk. Let tj≤Ajt_j \le A_jtj​≤Aj​ be natural numbers, and suppose that FFF vanishes to order at least nnn at every grid point ∑jmj′yj\sum_j m'_j y_j∑j​mj′​yj​ with mj′<tjm'_j < t_jmj′​<tj​. Let u≥2u \ge 2u≥2 and Z≥(∑jAj∣yj∣+1)(u+1)Z \ge \big(\sum_j A_j |y_j| + 1\big)(u + 1)Z≥(∑j​Aj​∣yj​∣+1)(u+1). Then at every point w=∑jmjyjw = \sum_j m_j y_jw=∑j​mj​yj​ with mj<Ajm_j < A_jmj​<Aj​, and for every rrr,

∣F(r)(w)∣≤2 r! (u−1)−n∏jtj(∑k∈s∣ck∣)ZEeWZ.|F^{(r)}(w)| \le 2\, r!\, (u - 1)^{-n \prod_j t_j} \Big(\sum_{k \in s} |c_k|\Big) Z^{E} e^{WZ}.∣F(r)(w)∣≤2r!(u−1)−n∏j​tj​(k∈s∑​∣ck​∣)ZEeWZ.

This is the analytic step of the extrapolation arguments: the ∏jtj\prod_j t_j∏j​tj​ grid points are distinct because the yjy_jyj​ are Q\mathbb{Q}Q-linearly independent, and the Cauchy estimate with zeros (FourExp.cauchy_estimate_with_zeros) is applied on a circle of radius (ρ+1)u(\rho + 1)u(ρ+1)u about www, where ρ=∑jAj∣yj∣\rho = \sum_j A_j |y_j|ρ=∑j​Aj​∣yj​∣.

Preamble
import Mathlib
Formal statement
namespace Transcendence

theorem expPoly_grid_estimate {ι κ : Type*} [Fintype ι] (y : ι → ℂ)
    (hy : LinearIndependent ℚ y) (s : Finset κ) (c ω : κ → ℂ) (e : κ → ℕ) (F : ℂ → ℂ)
    (hF : ∀ z, F z = ∑ k ∈ s, c k * z ^ e k * Complex.exp (ω k * z))
    (W : ℝ) (E : ℕ) (hω : ∀ k ∈ s, ‖ω k‖ ≤ W) (he : ∀ k ∈ s, e k ≤ E)
    (t A : ι → ℕ) (htA : ∀ j, t j ≤ A j) (n : ℕ)
    (hvan : ∀ m : ι → ℕ, (∀ j, m j < t j) → ∀ i < n,
      iteratedDeriv i F (∑ j, (m j : ℂ) * y j) = 0)
    (u Z : ℝ) (hu : 2 ≤ u) (hZ : (∑ j, (A j : ℝ) * ‖y j‖ + 1) * (u + 1) ≤ Z)
    (m : ι → ℕ) (hm : ∀ j, m j < A j) (r : ℕ) :
    ‖iteratedDeriv r F (∑ j, (m j : ℂ) * y j)‖
      ≤ (r.factorial : ℝ) * 2 * (1 / (u - 1)) ^ ((∏ j, t j) * n) *
        ((∑ k ∈ s, ‖c k‖) * Z ^ E * Real.exp (W * Z)) := by
  sorry

end Transcendence
Source
The analytic step of the extrapolation in the proof of Lemma 5 of M. Waldschmidt, Solution du huitième problème de Schneider, J. Number Theory 5 (1973), 191–202, and of the six exponentials theorem (S. Lang, Introduction to Transcendental Numbers, 1966, Ch. 2); it rests on the estimate of M. Waldschmidt, Indépendance algébrique des valeurs de la fonction exponentielle, Bull. Soc. Math. France 99 (1971), 285–304, §4, inequality (4.3). Formal proof: Diaz modulus mission, 27 September 2026 (C. Perassi).

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