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eβ/πe^{\beta/\pi}eβ/π is transcendental for every non-zero real algebraic β\betaβ

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DiazModulus.recip_pi_not_log_imag_gamma

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

four-exponentialslogarithmsnumber-theorytranscendence

For every purely imaginary algebraic γ≠0\gamma \neq 0γ=0 --- that is, γ=iβ\gamma = i\betaγ=iβ with β\betaβ a non-zero real algebraic number --- the number eγ/(iπ)=eβ/πe^{\gamma/(i\pi)} = e^{\beta/\pi}eγ/(iπ)=eβ/π is transcendental.

Equivalently: 1/π1/\pi1/π is not an algebraic multiple of a real logarithm of an algebraic number; equivalently again, π≠β/log⁡α\pi \neq \beta/\log\alphaπ=β/logα for any non-zero real algebraic β\betaβ and any real algebraic α>0\alpha > 0α>0, α≠1\alpha \neq 1α=1. Because γ\gammaγ is purely imaginary, λ=γ/(iπ)\lambda = \gamma/(i\pi)λ=γ/(iπ) is real, so eλe^{\lambda}eλ is real and positive, and ≠1\neq 1=1 since λ≠0\lambda \neq 0λ=0. This is the half containing the single number e1/πe^{1/\pi}e1/π, and it is the Hermite--Lindemann-shaped half of the split.

How this sits under its parent. The parent is DiazModulus.recip_pi_not_log (b5a16bec-19d1-48b7-bd3b-09e62db3e432): no non-zero algebraic γ\gammaγ has γ/(iπ)∈L\gamma/(i\pi) \in \mathcal{L}γ/(iπ)∈L. This node and its sibling DiazModulus.recip_pi_not_log_real_gamma together imply the parent, and each is strictly weaker in quantifier shape.

That the two halves suffice is not a case distinction — the real axis and the imaginary axis do not cover Q‾×\overline{\mathbb{Q}}^{\times}Q​×. It is a consequence of the structure of

S0={γ∈Q‾:γ/(iπ)∈L},S_0 = \{\gamma \in \overline{\mathbb{Q}} : \gamma/(i\pi) \in \mathcal{L}\},S0​={γ∈Q​:γ/(iπ)∈L},

which is a Q\mathbb{Q}Q-subspace of Q‾\overline{\mathbb{Q}}Q​ closed under complex conjugation: closed under addition because eλ+μ=eλeμe^{\lambda+\mu}=e^{\lambda}e^{\mu}eλ+μ=eλeμ, under Q×\mathbb{Q}^{\times}Q×-scaling because e(a/b)λe^{(a/b)\lambda}e(a/b)λ is a root of Xb−(eλ)aX^{b}-(e^{\lambda})^{a}Xb−(eλ)a, and under conjugation because iπ‾=−iπ\overline{i\pi}=-i\piiπ=−iπ, so that γ‾/(iπ)=−γ/(iπ)‾\overline{\gamma}/(i\pi) = -\overline{\gamma/(i\pi)}γ​/(iπ)=−γ/(iπ)​ and eγ‾/(iπ)=eγ/(iπ)‾ −1e^{\overline{\gamma}/(i\pi)} = \overline{e^{\gamma/(i\pi)}}^{\,-1}eγ​/(iπ)=eγ/(iπ)−1. Hence if γ∈S0\gamma \in S_0γ∈S0​ then Re⁡γ∈S0\operatorname{Re}\gamma \in S_0Reγ∈S0​ and iIm⁡γ∈S0i\operatorname{Im}\gamma \in S_0iImγ∈S0​, and γ≠0\gamma \neq 0γ=0 forces one of them to be non-zero. The reduction is formalised and sorry-free.

Strength. Weaker than the parent, not known to be easier. Neither child is closable with anything in the environment, and neither is known to imply the other. Both follow from the strong four exponentials conjecture by the parent's own argument, applied to x=(1,λ)x=(1,\lambda)x=(1,λ), y=(1,iπ)y=(1,i\pi)y=(1,iπ).

Honesty check. The ambient class of this node is a set of algebraic numbers, so it is inhabited outright — no conjecture is involved in witnessing it. Witness: γ=i\gamma = iγ=i, which is algebraic (a root of X2+1X^{2}+1X2+1), non-zero and purely imaginary. Neither half is provably constant and neither is conjecturally vacuous; this is the first leaf of the mission for which the honesty check is free rather than delicate.

No redundant hypotheses. All three of γ\gammaγ algebraic, γ≠0\gamma \neq 0γ=0 and the axis condition are used.

Preamble
import Definitions.Def_DiazModulus

open Complex ComplexConjugate
Formal statement
namespace DiazModulus
theorem recip_pi_not_log_imag_gamma :
    ∀ γ : ℂ, IsAlgebraic ℚ γ → γ ≠ 0 → γ.re = 0 →
      ¬ IsAlgebraic ℚ (Complex.exp (γ / (((Real.pi : ℝ) : ℂ) * Complex.I))) := by sorry
end DiazModulus
Source
Imaginary-axis half of DiazModulus.recip_pi_not_log (b5a16bec-19d1-48b7-bd3b-09e62db3e432), obtained from the conjugation-stability of the Q-subspace {gamma in Qbar : gamma/(i pi) in L}. Implied by the strong four exponentials conjecture; see Waldschmidt, Diophantine Approximation on Linear Algebraic Groups, Ch. 11.

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