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Project-declaredLean 4.32.0 · mathlib@249c48c2

Residue c₄ mul residue eq neg c₆

WeierstrassCurve.residue_c₄_mul_residue_eq_neg_c₆

Plain-language statement

The key identity φc₄ · φ(t'² - 4n') = -φc₆ of the twisting datum (t', n'): if its residues satisfy the trace and norm relations cut out by the node polynomial (κ = 54 b₆ - 3 b₂ b₄ + a₂ c₄), then the discriminant identity splitPolynomial_discrim turns them into this identity.

Exact Lean statement

theorem residue_c₄_mul_residue_eq_neg_c₆ [E.HasMultiplicativeReduction R] (t' n' : R)
    (hA : residue R (E.integralModel R).c₄ * residue R t'
      + residue R ((E.integralModel R).a₁ * (E.integralModel R).c₄) = 0)
    (hB : residue R (E.integralModel R).c₄ * residue R n'
      + residue R (54 * (E.integralModel R).b₆
        - 3 * (E.integralModel R).b₂ * (E.integralModel R).b₄
        + (E.integralModel R).a₂ * (E.integralModel R).c₄) = 0) :
    residue R (E.integralModel R).c₄ * residue R (t' ^ 2 - 4 * n')
      = -residue R (E.integralModel R).c₆

Formal artifact

Lean source

Canonical source
Full Lean sourceLean 4
theorem residue_c₄_mul_residue_eq_neg_c₆ [E.HasMultiplicativeReduction R] (t' n' : R)    (hA : residue R (E.integralModel R).c₄ * residue R t'      + residue R ((E.integralModel R).a₁ * (E.integralModel R).c₄) = 0)    (hB : residue R (E.integralModel R).c₄ * residue R n'      + residue R (54 * (E.integralModel R).b₆        - 3 * (E.integralModel R).b₂ * (E.integralModel R).b₄        + (E.integralModel R).a₂ * (E.integralModel R).c₄) = 0) :    residue R (E.integralModel R).c₄ * residue R (t' ^ 2 - 4 * n')      = -residue R (E.integralModel R).c₆ := by  set c₄' := (E.integralModel R).c₄ with hc₄'  set κ' := 54 * (E.integralModel R).b₆ - 3 * (E.integralModel R).b₂ * (E.integralModel R).b₄    + (E.integralModel R).a₂ * c₄' with hκ'  simp only [map_mul] at hA  have hRid : ((E.integralModel R).a₁ * c₄') ^ 2 + 4 * c₄' * κ'      = -(c₄' * (E.integralModel R).c₆) := by    rw [hκ', hc₄']    exact splitPolynomial_discrim (E.integralModel R)  have hdisc := congrArg (residue R) hRid  simp only [map_add, map_mul, map_pow, map_neg, map_ofNat] at hdisc  apply mul_left_cancel₀ (residue_integralModel_c₄_ne_zero E R)  simp only [map_sub, map_mul, map_pow, map_ofNat]  linear_combination hdisc    + (residue R c₄' * residue R t' - residue R (E.integralModel R).a₁ * residue R c₄') * hA    - 4 * residue R c₄' * hB
Project
Fermat's Last Theorem
License
Apache-2.0
Commit
8dd808888295
Source
FLT/KnownIn1980s/EllipticCurves/QuadraticTwists/SplitMultiplicativeReduction.lean:237-260

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