If `f = ∑ cᵢ t^(d-i) xⁱ`, then in the chart `R[t/x]` the function `f` factors as `x^d · ∑ cᵢ (t/x)^(d-i)`, and the boundary contact of `f` with `t = 0` is `d` plus the contact of the strict transform
ProvedTypeDensity.boundary_contact_of_twisted_generatortype-density
If f = ∑ cᵢ t^(d-i) xⁱ, then in the chart R[t/x] the function f factors as x^d · ∑ cᵢ (t/x)^(d-i), and the boundary contact of f with t = 0 is d plus the contact of the strict transform with the slope divisor.
Preamble
import Definitions.Def_TypeDensity_Basic import Definitions.Def_TypeDensity_Formula_LawAlgebra import Definitions.Def_TypeDensity_Measure_AdicCylinders import Definitions.Def_TypeDensity_Measure_HenselProducts import Definitions.Def_TypeDensity_Surfaces_Lengths import Definitions.Def_TypeDensity_Surfaces_PowerSeries import Definitions.Def_TypeDensity_Formula_FiniteFieldCounts import Definitions.Def_TypeDensity_Formula_StateCombinatorics import Definitions.Def_TypeDensity_Blowup_Directions import Definitions.Def_TypeDensity_Unramified_Extension import Definitions.Def_TypeDensity_Blowup_Charts import Definitions.Def_TypeDensity_Algebra_AlgebraType import Definitions.Def_TypeDensity_Measure_PrimitiveLocus import Definitions.Def_TypeDensity_Algebra_FactorInvariant import Definitions.Def_TypeDensity_Surfaces_TruncatedSeries import Definitions.Def_TypeDensity_Surfaces_ConcreteAtlas import Definitions.Def_TypeDensity_Blowup_DivisorPoints import Theorems.Thm_TypeDensity_blowup_chart_relation import Theorems.Thm_TypeDensity_boundary_chart_quotient_equiv import Theorems.Thm_TypeDensity_quotient_ring_length_intrinsic import Theorems.Thm_TypeDensity_length_quotient_sup_mul_eq_add import Theorems.Thm_TypeDensity_length_quotient_sup_pow_eq_mul import Mathlib.FieldTheory.RatFunc.Basic import Mathlib.MeasureTheory.Measure.Haar.Unique import Mathlib.NumberTheory.ArithmeticFunction.Moebius import Mathlib.NumberTheory.Padics.PadicIntegers import Mathlib.RingTheory.IntegralClosure.IntegralRestrict import Mathlib.RingTheory.MvPowerSeries.Basic import Mathlib.RingTheory.RamificationInertia.Basic import Mathlib.Topology.Algebra.Nonarchimedean.AdicTopology import Mathlib.FieldTheory.Finite.GaloisField import Mathlib.RingTheory.AdicCompletion.Algebra import Mathlib.RingTheory.RegularLocalRing.Defs import Mathlib.Topology.Algebra.MvPolynomial import Mathlib.Algebra.Group.Pi.Units import Mathlib.Order.CompletePartialOrder import Mathlib.RingTheory.Henselian import Mathlib.RingTheory.Polynomial.Resultant.Basic import Mathlib.RingTheory.SimpleRing.Principal import Mathlib.FieldTheory.Finite.Extension import Mathlib.RingTheory.AdicCompletion.Noetherian import Mathlib.RingTheory.MvPowerSeries.Equiv import Mathlib.RingTheory.PicardGroup import Mathlib.FieldTheory.RatFunc.AsPolynomial import Mathlib.RingTheory.AdicCompletion.Completeness import Mathlib.Algebra.GroupWithZero.Submonoid.CancelMulZero import Mathlib.Algebra.Module.StablyFree.Basic import Mathlib.NumberTheory.Padics.RingHoms import Mathlib.Algebra.Azumaya.Basic import Mathlib.RingTheory.AdicCompletion.RingHom import Mathlib.RingTheory.TotallySplit import Mathlib.RingTheory.AdicCompletion.LocalRing import Mathlib.RingTheory.KrullDimension.NonZeroDivisors import Mathlib.Algebra.Group.NatPowAssoc set_option autoImplicit false open TypeDensity open scoped BigOperators ENNReal
Formal statement
theorem TypeDensity.boundary_contact_of_twisted_generator (R : Type) [CommRing R] (t x : R)
[(Ideal.span ({t,x} : Set R)).IsMaximal] (hreg : RegularParameterPair R t x) (d : ℕ) (f : R)
(c : Fin (d + 1) → R) (hc : f = ∑ i : Fin (d + 1), c i * t ^ (d - i.val) * x ^ i.val) :
algebraMap R (BlowupChart R x t) f = (chartBase R x t x)^d *
∑ i : Fin (d+1), algebraMap R (BlowupChart R x t) (c i) * (chartSlope R x t)^(d - i.val) ∧
Module.length R (R ⧸ (Ideal.span {f} ⊔ Ideal.span {t})) = (d : ℕ∞) +
Module.length (BlowupChart R x t) (BlowupChart R x t ⧸
(Ideal.span {∑ i : Fin (d+1), algebraMap R (BlowupChart R x t) (c i) *
(chartSlope R x t)^(d - i.val)} ⊔ Ideal.span {chartSlope R x t})) := by sorrySource
TypeDensity/Blowup/DivisorPoints.lean#L92-L149