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Project-declaredLean 4.32.0 · mathlib@249c48c2

Quadratic Twist Point Equiv map

WeierstrassCurve.quadraticTwistPointEquiv_map

Plain-language statement

Naturality of quadraticTwistPointEquiv in M: the isomorphisms on M-points over varying M ⊇ L are all induced by a single isomorphism of curves over L, so they commute with the maps on points induced by any L-algebra homomorphism.

Exact Lean statement

theorem quadraticTwistPointEquiv_map {N : Type*} [Field N] [Algebra K N] [Algebra L N]
    [IsScalarTower K L N] [DecidableEq N] (f : M →ₐ[L] N)
    (P : ((E.quadraticTwist L)⁄M).Point) :
    E.quadraticTwistPointEquiv L N (Affine.Point.map f P) =
      Affine.Point.map f (E.quadraticTwistPointEquiv L M P)

Formal artifact

Lean source

Canonical source
Full Lean sourceLean 4
theorem quadraticTwistPointEquiv_map {N : Type*} [Field N] [Algebra K N] [Algebra L N]    [IsScalarTower K L N] [DecidableEq N] (f : M ₐ[L] N)    (P : ((E.quadraticTwist L)⁄M).Point) :    E.quadraticTwistPointEquiv L N (Affine.Point.map f P) =      Affine.Point.map f (E.quadraticTwistPointEquiv L M P) := by  -- The base-changed change of variables over `N` is the image under `f` of that over `M`.  have hu : (((E.quadraticTwistVarChange L).baseChange N).u : N)      = f (((E.quadraticTwistVarChange L).baseChange M).u : M) := by    simp only [VariableChange.baseChange, VariableChange.map, Units.coe_map, MonoidHom.coe_coe]    exact (f.commutes _).symm  have hr : ((E.quadraticTwistVarChange L).baseChange N).r      = f ((E.quadraticTwistVarChange L).baseChange M).r := (f.commutes _).symm  have hs : ((E.quadraticTwistVarChange L).baseChange N).s      = f ((E.quadraticTwistVarChange L).baseChange M).s := (f.commutes _).symm  have ht : ((E.quadraticTwistVarChange L).baseChange N).t      = f ((E.quadraticTwistVarChange L).baseChange M).t := (f.commutes _).symm  rcases P with _ | x, y, h  · simp [ Affine.Point.zero_def]  · simp only [quadraticTwistPointEquiv, AddEquiv.trans_apply, Affine.Point.equivOfEq_some,      Affine.Point.equivVariableChange_some, Affine.Point.map_some]    refine Affine.Point.some_eq_some (E.baseChange N) ?_ ?_    · simp only [map_add, map_mul, map_pow, hu, hr]    · simp only [map_add, map_mul, map_pow, hu, hs, ht]
Project
Fermat's Last Theorem
License
Apache-2.0
Commit
8dd808888295
Source
FLT/KnownIn1980s/EllipticCurves/QuadraticTwists/QuadraticTwists.lean:665-687

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