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Consequences of the Gauss-Jacobi identities and cubic reciprocity

Proved
QRH.gauss_jacobi_consequences

by Lucas · Oct 20, 2026 · Mathlib 0df444a (Lean v4.33.1)

cubicreciprocitygausssumsmobiusfunctionrayclassgroup

Let a, b, n be squarefree primary elements prime to S, with a and b coprime in the sense that their only common divisor is the unit. Then the interface axioms imply the four conversion identities of Lemma 4.1 of the source: first, conj(alpha n) gamma_2(n) gamma_1(n) = mu(n) G(cl n); second, mu(n) gamma_{-1}(n) = chi_n(-1) G(cl n)^{-1} conj(alpha n) gamma_2(n); third, the quotient identity chi_a(-1) conj(G(cl a)) G(cl b) R(cl a, cl b) = G(cl b inv(cl a)) in the ray class group; and fourth, the multiplicativity of the cubic Gauss-sum coefficients up to a sextic twist: a_xi(ab) = a_xi(a) a_xi(b) chi_b(a)^4.

Preamble
import Mathlib
import Definitions.Def_QRH_arith
import Definitions.Def_QRH_sums
import Definitions.Def_QRH_lfun
Formal statement
universe u

namespace QRH

/-- The consequences of the Gauss-Jacobi identities and cubic
reciprocity (Lemma 4.1 of the source), for squarefree primary elements
prime to S. The four conjuncts are the conversion identities between
Möbius coefficients and cubic Gauss sums (equations 4.7 and 4.8): the
Möbius factor combines with the Poisson γ₋₁ into the cubic coefficient,
and back; the quotient identity for the ray class factor G (equation
4.9); and the multiplicativity of the cubic Gauss-sum coefficients a_ξ
up to a sextic twist (equation 4.10). Each follows from the interface
axioms by complex algebra: the Gauss sums and the phase have modulus one,
Möbius squares to one on squarefree elements, and the reciprocity
bicharacter is real. -/
theorem gauss_jacobi_consequences (W : QRHWorld.{u}) (a b n : W.E)
    (hsn : W.IsSqf n) (hgn : W.Sgood n)
    (hsa : W.IsSqf a) (hga : W.Sgood a)
    (hsb : W.IsSqf b) (hgb : W.Sgood b)
    (hcop : ∀ d : W.E, d ∈ W.divs a → d ∈ W.divs b → d = W.one) :
    star (W.alpha n) * W.gamma 2 n * W.gamma 1 n
        = W.mu n * W.Gcl (W.cl n)
      ∧ W.mu n * W.gamma (-1) n
        = W.chiNeg n * (W.Gcl (W.cl n))⁻¹ * star (W.alpha n)
            * W.gamma 2 n
      ∧ W.chiNeg a * star (W.Gcl (W.cl a)) * W.Gcl (W.cl b)
            * W.Rcl (W.cl a) (W.cl b)
          = W.Gcl (W.mulC (W.cl b) (W.invC (W.cl a)))
      ∧ axi W (W.mul a b) = axi W a * axi W b * W.chi b a ^ 4 := by
  sorry

end QRH
Source
The Quasi-Riemann Hypothesis, October 2026, Lemma 4.1 (equations 4.7-4.10).
Read-back

What the Lean code literally says, in plain math · glm-5-latest-short

Read-back (self-check authored by the same model that produced the statement): the formal theorem asserts, for squarefree primary a, b, n prime to S with a and b sharing no divisor but the unit, the conjunction of four complex equalities in the world W: (1) star(alpha n) * gamma 2 n * gamma 1 n = mu n * G(cl n); (2) mu n * gamma(-1) n = chiNeg n * (G(cl n))^{-1} * star(alpha n) * gamma 2 n; (3) chiNeg a * star(G(cl a)) * G(cl b) * Rcl(cl a)(cl b) = G(mulC (cl b) (invC (cl a))); (4) axi W (mul a b) = axi W a * axi W b * chi b a^4, where axi W x = star(W.alpha x) * W.gamma 2 x * W.xi x. Each conjunct is derivable from the modulus-one fields (alpha_abs, gamma_abs, Gcl_abs, chiNeg_abs, Rcl_abs), the Gauss-Jacobi fields (gamma_1_2, gamma_1_m1, gamma_2_cube), Mobius squaring (mu_sqf), the cocycle identity (Gcl_mul), the inverse identity (Gcl_invC), and the multiplicativity fields (alpha_mul, xi_mul, gamma_2_mul, chi_mul_den, chi_mul_num, recip_cubic).

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