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Gel'fond-type transcendence criterion with continuous growth functions

Proved
FourExp.transcendence_criterion_continuous

by carlok · Sep 15, 2026 · Mathlib 0df444a (Lean v4.33.1)

diophantine-approximationnumber-theorytranscendence

The transcendence criterion, for continuous growth functions.

This is FourExp.transcendence_criterion with two changes. The functions σ1,σ2\sigma_1, \sigma_2σ1​,σ2​ are also assumed continuous. The conditions

σ2(x)≤σ1(x),σi(x+1)≤ai σi(x)\sigma_2(x) \le \sigma_1(x), \qquad \sigma_i(x+1) \le a_i\,\sigma_i(x)σ2​(x)≤σ1​(x),σi​(x+1)≤ai​σi​(x)

are required only for x≥1x \ge 1x≥1, not for x>0x > 0x>0.

Explicitly: let α∈C\alpha \in \mathbb{C}α∈C and ε>0\varepsilon > 0ε>0. Let σ1,σ2\sigma_1, \sigma_2σ1​,σ2​ be continuous, strictly increasing and unbounded, and let a1,a2≥1a_1, a_2 \ge 1a1​,a2​≥1 satisfy the conditions above for x≥1x \ge 1x≥1. Suppose that for all N>N0N > N_0N>N0​ there is a non-zero PN∈Z[X]P_N \in \mathbb{Z}[X]PN​∈Z[X] with coefficients at most eσ1(N)e^{\sigma_1(N)}eσ1​(N), degree at most σ2(N)\sigma_2(N)σ2​(N), and ∣PN(α)∣<exp⁡(−Cσ1(N)σ2(N))|P_N(\alpha)| < \exp(-C\sigma_1(N)\sigma_2(N))∣PN​(α)∣<exp(−Cσ1​(N)σ2​(N)), where C=max⁡{10+ε,(4+ε)a1a2}C = \max\{10+\varepsilon, (4+\varepsilon)a_1a_2\}C=max{10+ε,(4+ε)a1​a2​}. Then α\alphaα is algebraic.

Why this form. Waldschmidt's proof (1971, §3) inverts σi\sigma_iσi​: it defines zq=max⁡(σ1−1(13log⁡hq), σ2−1((1+ε2)−1δq))z_q = \max\bigl(\sigma_1^{-1}(\tfrac13\log h_q),\ \sigma_2^{-1}((1+\tfrac\varepsilon2)^{-1}\delta_q)\bigr)zq​=max(σ1−1​(31​loghq​), σ2−1​((1+2ε​)−1δq​)) and uses σi(σi−1(y))=y\sigma_i(\sigma_i^{-1}(y)) = yσi​(σi−1​(y))=y, which needs continuity. The paper notes that continuity can be assumed, since only integer values matter. That step is the accepted reduction from FourExp.transcendence_criterion, by piecewise-linear interpolation. The proof only ever uses large xxx, so asking the conditions for x≥1x \ge 1x≥1 loses nothing, and interpolation cannot preserve them on (0,1)(0, 1)(0,1) in general.

Intended proof. The 1971 argument, using Gel'fond's height inequality for a divisor, Gel'fond's small-irreducible-factor lemma, and the resultant bound that forces Qq∣PNQ_q \mid P_NQq​∣PN​.

Preamble
import Mathlib

open Filter Topology
Formal statement
namespace FourExp

theorem transcendence_criterion_continuous
    (α : ℂ) (ε : ℝ) (hε : 0 < ε)
    (σ₁ σ₂ : ℝ → ℝ) (hσ₁ : StrictMono σ₁) (hσ₂ : StrictMono σ₂)
    (hσ₁c : Continuous σ₁) (hσ₂c : Continuous σ₂)
    (hσ₁t : Tendsto σ₁ atTop atTop) (hσ₂t : Tendsto σ₂ atTop atTop)
    (a₁ a₂ : ℝ) (ha₁ : 1 ≤ a₁) (ha₂ : 1 ≤ a₂)
    (h₂₁ : ∀ x : ℝ, 1 ≤ x → σ₂ x ≤ σ₁ x)
    (hgrowth₁ : ∀ x : ℝ, 1 ≤ x → σ₁ (x + 1) ≤ a₁ * σ₁ x)
    (hgrowth₂ : ∀ x : ℝ, 1 ≤ x → σ₂ (x + 1) ≤ a₂ * σ₂ x)
    (N₀ : ℕ) (P : ℕ → Polynomial ℤ)
    (hP_ne : ∀ N : ℕ, N₀ < N → P N ≠ 0)
    (hP_height : ∀ N : ℕ, N₀ < N → ∀ i : ℕ, |((P N).coeff i : ℝ)| ≤ Real.exp (σ₁ N))
    (hP_deg : ∀ N : ℕ, N₀ < N → ((P N).natDegree : ℝ) ≤ σ₂ N)
    (hP_small : ∀ N : ℕ, N₀ < N →
      ‖Polynomial.aeval α (P N)‖ <
        Real.exp (-(max (10 + ε) ((4 + ε) * (a₁ * a₂)) * σ₁ N * σ₂ N))) :
    IsAlgebraic ℚ α := by
  sorry

end FourExp
Source
M. Waldschmidt, Indépendance algébrique des valeurs de la fonction exponentielle, Bull. Soc. Math. France 99 (1971), 285–304, §3, Lemme fondamental and its proof (continuity of σᵢ is assumed there without loss of generality).

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