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Cross Block scaled det norm sq

Proved
D1Bound5.crossBlock_scaled_det_norm_sq

by tp · Oct 23, 2026 · Mathlib 0df444a (Lean v4.33.1)

diophantine-tuplesnumber-theory

Squared modulus of the cross-block determinant after the two scaling steps. Stating the identity with squares avoids real square-root choices.

Preamble
import Mathlib.Algebra.QuadraticAlgebra.Basic
import Mathlib.Algebra.Ring.Basic
import Mathlib.Algebra.Ring.Equiv
import Mathlib.Analysis.Complex.Basic
import Mathlib.Analysis.Complex.Norm
import Mathlib.Analysis.Complex.Polynomial.Basic
import Mathlib.Data.Complex.Basic
import Mathlib.Data.Finset.Card
import Mathlib.Data.Int.GCD
import Mathlib.LinearAlgebra.Dimension.Free
import Mathlib.LinearAlgebra.Matrix.Determinant.Basic
import Mathlib.LinearAlgebra.Matrix.ToLinearEquiv
import Mathlib.NumberTheory.NumberField.InfinitePlace.TotallyRealComplex
import Mathlib.NumberTheory.NumberField.Norm
import Mathlib.Tactic.FieldSimp
import Mathlib.Tactic.FinCases
import Mathlib.Tactic.GCongr
import Mathlib.Tactic.Linarith
import Mathlib.Tactic.LinearCombination
import Mathlib.Tactic.NormNum
import Mathlib.Tactic.Ring

Formal statement
section
open scoped BigOperators NumberField
open Module

namespace D1Bound5




theorem _root_.D1Bound5.crossBlock_scaled_det_norm_sq
    {R : Type*} [CommRing R] (f : R →+* ℂ)
    (a b : Fin 3 → R) (u v : Fin 3 → ℂ)
    (S : Fin 3 → Fin 3 → R)
    (hu : ∀ i, (u i)^2 = f (a i)) (hv : ∀ j, (v j)^2 = f (b j)) :
    ‖Matrix.det (Matrix.of (fun i j => (f (a i)*u i)*f (S i j)*(f (b j)*v j)))‖^2 =
      ((‖f (a 0)‖*‖f (b 0)‖)*(‖f (a 1)‖*‖f (b 1)‖)*
        (‖f (a 2)‖*‖f (b 2)‖))^3*‖f (Matrix.det (Matrix.of S))‖^2 := by sorry







end D1Bound5
end
Source
D1Bound5/CrossBlockTuple.lean, lines 41-84, SHA-256 4f7736bd25878caf4f646f90a08781588133d8497db784873e94a7e8e819b915. Project: https://github.com/tomislav-math/d1-bound5-lean

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