Quadratic Twist Point Equiv map of not fixed
WeierstrassCurve.quadraticTwistPointEquiv_map_of_not_fixed
Plain-language statement
The anti-equivariance underlying quadraticTwistPointEquiv_galois: if σ ∈ Aut(M/K) does not fix L pointwise (χ(σ) = -1), then transporting its action through Eᴸ(M) ≅ E(M) gives minus its action. This is the point-level shadow of quadraticTwistVarChange_baseChange_map.
Exact Lean statement
theorem quadraticTwistPointEquiv_map_of_not_fixed {σ : M ≃ₐ[K] M}
(hσ : ¬ ∀ x : L, σ (algebraMap L M x) = algebraMap L M x)
(P : ((E.quadraticTwist L)⁄M).Point) :
E.quadraticTwistPointEquiv L M (Affine.Point.map σ.toAlgHom P) =
-Affine.Point.map σ.toAlgHom (E.quadraticTwistPointEquiv L M P)Formal artifact
Lean source
theorem quadraticTwistPointEquiv_map_of_not_fixed {σ : M ≃ₐ[K] M} (hσ : ¬ ∀ x : L, σ (algebraMap L M x) = algebraMap L M x) (P : ((E.quadraticTwist L)⁄M).Point) : E.quadraticTwistPointEquiv L M (Affine.Point.map σ.toAlgHom P) = -Affine.Point.map σ.toAlgHom (E.quadraticTwistPointEquiv L M P) := by have hM := E.quadraticTwistVarChange_baseChange_map L M hσ have hu : σ.toAlgHom (((E.quadraticTwistVarChange L).baseChange M).u : M) = -(((E.quadraticTwistVarChange L).baseChange M).u : M) := by simpa [VariableChange.mul_def, negVariableChange] using congrArg (fun C ↦ (VariableChange.u C : M)) hM have hr : σ.toAlgHom ((E.quadraticTwistVarChange L).baseChange M).r = ((E.quadraticTwistVarChange L).baseChange M).r := by simpa [VariableChange.mul_def, negVariableChange] using congrArg VariableChange.r hM have hs : σ.toAlgHom ((E.quadraticTwistVarChange L).baseChange M).s = -((E.quadraticTwistVarChange L).baseChange M).s - (E.baseChange M).a₁ := by simpa [VariableChange.mul_def, negVariableChange, sub_eq_add_neg] using congrArg VariableChange.s hM have ht : σ.toAlgHom ((E.quadraticTwistVarChange L).baseChange M).t = -((E.quadraticTwistVarChange L).baseChange M).t - ((E.quadraticTwistVarChange L).baseChange M).r * (E.baseChange M).a₁ - (E.baseChange M).a₃ := by simpa [VariableChange.mul_def, negVariableChange, sub_eq_add_neg, mul_neg_one, (by ring : ((-1 : M)) ^ 3 = -1)] using congrArg VariableChange.t hM rcases P with _ | ⟨x, y, hns⟩ · simp [← Affine.Point.zero_def] · simp only [quadraticTwistPointEquiv, AddEquiv.trans_apply, Affine.Point.equivOfEq_some, Affine.Point.equivVariableChange_some, Affine.Point.map_some, Affine.Point.neg_some] refine Affine.Point.some_eq_some (E.baseChange M) ?_ ?_ · simp only [map_add, map_mul, map_pow, hu, hr] ring · simp only [Affine.negY, map_add, map_mul, map_pow, hu, hr, hs, ht] ring- Project
- Fermat's Last Theorem
- License
- Apache-2.0
- Commit
- 8dd808888295
- Source
- FLT/KnownIn1980s/EllipticCurves/QuadraticTwists/QuadraticTwists.lean:692-723
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