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Laurent hulls: for u transcendental over a subfield K of ℂ and a finite S ⊆ ℤ, span_K{u^s : s ∈ S} carries a p×q configuration iff S contains a sumset A + B with |A| = p, |B| = q

Proved
DiazModulus.laurent_hull_config_iff

by carlok · Oct 8, 2026 · Mathlib 0df444a (Lean v4.33.1)

combinatoricsdiaz-modulus-leantranscendence

A p×qp \times qp×q configuration over a field KKK in a KKK-subspace V⊆CV \subseteq \mathbb{C}V⊆C is a pair x1,…,xpx_1, \dots, x_px1​,…,xp​ and y1,…,yqy_1, \dots, y_qy1​,…,yq​ of complex numbers, each family linearly independent over KKK, with every product xiyjx_iy_jxi​yj​ in VVV; it is the input of Roy's strong six exponentials theorem when p=2p = 2p=2, q=3q = 3q=3, K=Q‾K = \overline{\mathbb{Q}}K=Q​ and V=L~V = \widetilde{\mathcal{L}}V=L.

Let KKK be a subfield of C\mathbb{C}C and uuu transcendental over KKK. For a set SSS of integers write VS=span⁡K{us:s∈S}V_S = \operatorname{span}_K\{u^s : s \in S\}VS​=spanK​{us:s∈S} (the Laurent hull of SSS). For a finite SSS and p,q≥1p, q \ge 1p,q≥1, VSV_SVS​ carries a p×qp \times qp×q configuration over KKK if and only if there are A,B⊆ZA, B \subseteq \mathbb{Z}A,B⊆Z with ∣A∣=p|A| = p∣A∣=p, ∣B∣=q|B| = q∣B∣=q and A+B⊆SA + B \subseteq SA+B⊆S.

At a candidate uuu, uk∈L~u^k \in \widetilde{\mathcal{L}}uk∈L brings u−k=ρ−k uk‾∈L~u^{-k} = \rho^{-k}\,\overline{u^k} \in \widetilde{\mathcal{L}}u−k=ρ−kuk∈L, so hypotheses on powers of uuu put Laurent hulls inside L~\widetilde{\mathcal{L}}L; this criterion says exactly when Roy's strong six exponentials theorem can refute them through those hulls. The case S={0,±1,±k}S = \{0, \pm 1, \pm k\}S={0,±1,±k} is DiazModulus.power_hull_strong_six_exp_configuration_iff.

Proof. If A+B⊆SA + B \subseteq SA+B⊆S, take xi=uaix_i = u^{a_i}xi​=uai​, yj=ubjy_j = u^{b_j}yj​=ubj​; distinct integer powers of uuu are independent. Conversely, choose NNN with S+N⊆NS + N \subseteq \mathbb{N}S+N⊆N and polynomials PijP_{ij}Pij​ supported on S+NS + NS+N with Pij(u)=uNxiyjP_{ij}(u) = u^Nx_iy_jPij​(u)=uNxi​yj​. The spans VVV of the Pi1P_{i1}Pi1​ and WWW of the P1jP_{1j}P1j​ have dimensions ppp and qqq, hence (DiazModulus.polynomial_submodule_trailing_degrees_card) exactly ppp and qqq orders at 000. For f∈Vf \in Vf∈V, g∈Wg \in Wg∈W, fg=P11hfg = P_{11}hfg=P11​h with hhh a combination of the PijP_{ij}Pij​ (both sides agree at uuu), so ord⁡f+ord⁡g−ord⁡P11−N∈S\operatorname{ord} f + \operatorname{ord} g - \operatorname{ord} P_{11} - N \in Sordf+ordg−ordP11​−N∈S; shifting the order set of VVV gives AAA, and the order set of WWW is BBB.

Novelty. Not found in the sources read. The nearest printed results are the progression lemma of Fischler (2001, Lemma 6.1) and its repetition in Diaz (2007, Th. 7(2)); the library had the single family S={0,±1,±k}S = \{0, \pm1, \pm k\}S={0,±1,±k}.

Preamble
import Definitions.Def_DiazModulus
Formal statement
open Complex ComplexConjugate

namespace DiazModulus

open Pointwise in
theorem laurent_hull_config_iff (K : Subfield ℂ) (u : ℂ) (hT : Transcendental K u)
    (S : Finset ℤ) (p q : ℕ) (hp : 1 ≤ p) (hq : 1 ≤ q) :
    (∃ (x : Fin p → ℂ) (y : Fin q → ℂ), LinearIndependent K x ∧ LinearIndependent K y ∧
      ∀ i j, x i * y j ∈ Submodule.span K ((fun s : ℤ => u ^ s) '' (S : Set ℤ))) ↔
    ∃ A B : Finset ℤ, A.card = p ∧ B.card = q ∧ A + B ⊆ S := by
  sorry

end DiazModulus
Source
Not found in the sources read; generalises DiazModulus.power_hull_strong_six_exp_configuration_iff. Nearest: S. Fischler, Orbits under algebraic groups and logarithms of algebraic numbers, Acta Arith. 100 (2001), 167–187, Lemma 6.1 (p. 184). R6 of the Diaz modulus mission (the polar-degree note). Formal proof: Diaz modulus mission, 8 October 2026 (C. Perassi).

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