The powered-image auxiliary family with exchanged coordinates #
The existing powered-image theorem orients the auxiliary family as
(x^m,y^n). Proposition 2 is applied with the smaller source height first,
so this module supplies the equally canonical orientation (y^n,x^m).
It uses the untransposed powered-image equation and the first-coordinate
Frobenius power basis.
theorem
BGS.CorvajaZannier.poweredCoordinateFrobeniusImage_auxiliaryFamily_linearIndependent_swapped
{K : Type u_1}
[Field K]
[PerfectField K]
{p : ℕ}
[Fact (Nat.Prime p)]
[CharP K p]
{f : MvPolynomial (Fin 2) K}
(habsolute : Irreducible ((MvPolynomial.map (algebraMap K (AlgebraicClosure K))) f))
(hf : Irreducible f)
(hpartialFirst : (MvPolynomial.pderiv 0) f ≠ 0)
(hpartialSecond : (MvPolynomial.pderiv 1) f ≠ 0)
(m n : ℕ)
(hm : 0 < m)
(hn : 0 < n)
(hmPrime : ¬p ∣ m)
(h k : ℕ)
(hh : 0 < h)
(hk : 0 < k)
(hsize :
let F := frobeniusSubfield (PlaneCurveFunctionField f) p;
have ι := perfectConstantsToFrobeniusSubfield;
have g := Polynomial.map (Polynomial.mapRingHom ι) (poweredCoordinateImageRelation hf hpartialSecond m hm n);
g.natDegree * h + (transposeBivariate g).natDegree * k < p)
(hexcluded :
let F := frobeniusSubfield (PlaneCurveFunctionField f) p;
have ι := perfectConstantsToFrobeniusSubfield;
have g := Polynomial.map (Polynomial.mapRingHom ι) (poweredCoordinateImageRelation hf hpartialSecond m hm n);
¬(g.natDegree ≤ k ∧ (transposeBivariate g).natDegree ≤ h))
:
LinearIndependent (↥(frobeniusSubfield (PlaneCurveFunctionField f) p))
(auxiliaryFamily (planeCurveFunction f 1 ^ n) (planeCurveFunction f 0 ^ m) h k)
Proposition 1 for the powered coordinates in the exchanged orientation. The relation degrees are those of the untransposed powered-image equation.