Module

GenusOneDivisors.lean

Nyll.AlgebraicCurves.Cohomology.RiemannRoch.GenusOneDivisors
4 declarations indexed from sourceView source ↗

Degree-one divisor classes in genus one

Riemann--Roch supplies a nonzero section of every degree-one divisor. Its effective divisor is a single place. The same dimension calculation proves uniqueness: a function with at most one simple pole must be constant.

Declarations

AlgebraicCurve.Divisor.exists_single_of_effective_degree_one

An effective divisor of degree one over an algebraically closed constant field is the divisor of a single place.

Source context 3 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
namespace AlgebraicCurve
variable {K F : Type*} [Field K] [IsAlgClosed K] [Field F] [Algebra K F]
  [IsCurveOver K F]
theorem Divisor.exists_single_of_effective_degree_one (D : Divisor K F)
    (hD : ∀ v : Place K F, 0 ≤ D v) (hdegree : D.degree = 1) :
    ∃ p : Place K F, D = Finsupp.single p 1
AlgebraicCurve.ell_eq_one_of_genus_one_degree_one

In genus one, every degree-one divisor has exactly one independent section.

Source context 4 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
namespace AlgebraicCurve
variable {K F : Type*} [Field K] [IsAlgClosed K] [Field F] [Algebra K F]
  [IsCurveOver K F]
variable [Algebra.EssFiniteType K F]
theorem ell_eq_one_of_genus_one_degree_one (hg : genusFF K F = 1)
    (D : Divisor K F) (hD : D.degree = 1) : ell D = 1
AlgebraicCurve.eq_of_single_sub_single_principal_of_genus_one

Two places on a genus-one function field cannot differ by a principal divisor unless they are the same place.

Source context 4 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
namespace AlgebraicCurve
variable {K F : Type*} [Field K] [IsAlgClosed K] [Field F] [Algebra K F]
  [IsCurveOver K F]
variable [Algebra.EssFiniteType K F]
theorem eq_of_single_sub_single_principal_of_genus_one (hg : genusFF K F = 1)
    (p q : Place K F) (h : Divisor.IsPrincipal (Finsupp.single p 1 - Finsupp.single q 1)) :
    p = q
AlgebraicCurve.existsUnique_place_principal_sub_of_genus_one

Every degree-one divisor on a genus-one function field is linearly equivalent to exactly one place. Neither an effective representative nor its uniqueness is input.

Source context 4 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
namespace AlgebraicCurve
variable {K F : Type*} [Field K] [IsAlgClosed K] [Field F] [Algebra K F]
  [IsCurveOver K F]
variable [Algebra.EssFiniteType K F]
theorem existsUnique_place_principal_sub_of_genus_one (hg : genusFF K F = 1)
    (D : Divisor K F) (hD : D.degree = 1) :
    ∃! p : Place K F, Divisor.IsPrincipal (Finsupp.single p 1 - D)