The local model near a simple point is a manifold #
Hironaka's "by means of jacobian criterion and the implicit function theorem"
[Hir64, Ch. 0, §1, p. 121]: at a point z of the local model X = V(f) ⊆ G ⊆ Kⁿ with the chart
data of Hironaka/AnalyticSpace/ModelChart.lean (an adapted chart e with (f) = (e_σ) near z),
the open X|V over the good neighbourhood W is K-isomorphic to the open G' ⊆ K^{n−c},
G' = {v | ι_σ v ∈ e.target, e⁻¹(ι_σ v) ∈ W} with ι_σ = embedCompl σ the coordinate subspace
(exists_kIso_analyticSpaceOfOpen_of_span_germ_eq). This file builds the underlying homeomorphism
G' ≃ₜ V (v ↦ e⁻¹(ι_σ v), inverse w ↦ π_σ(e w)), the evaluation of the fibres
𝒜_{G,y}/𝓘_y → K of the quotient sheaf (well defined because 𝓘_y ⊆ 𝔪_y) through which the
K-morphism (G', 𝒜_{G'}) → X|V acts on sections, and proves it a K-isomorphism: its stalk
maps are surjective (a germ on G' pulls back along π_σ ∘ e) and injective (a surjection
between regular local rings of the same dimension n − c is an isomorphism). Used by
Hironaka/AnalyticSpace/Jacobian.lean and Hironaka/AnalyticSpace/RegEval.lean.
The open V ∋ z of the local model lying over the good neighbourhood W.
Equations
- D.V = (TopologicalSpace.Opens.map (↑(AnalyticSpace.localModel.ι K n G f)).base).obj D.W
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The map K^{n−c} → Kⁿ, v ↦ e⁻¹(ι_σ v) (junk outside e.target).
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The coordinate-subspace inclusion ι_σ : K^{n−c} → Kⁿ, continuous.
The open G' ⊆ K^{n−c}: the points v with ι_σ v ∈ e.target and e⁻¹(ι_σ v) ∈ W.
Equations
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The underlying map G' → V, v ↦ e⁻¹(ι_σ v).
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The inverse map V → G', w ↦ π_σ(e w).
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The inclusion V → Kⁿ, w ↦ w, is inducing (three subtype layers).
The homeomorphism G' ≃ₜ V of Hironaka's implicit-function-theorem step.
Equations
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Evaluation of the fibres of the quotient sheaf #
The stalk 𝒜_{G,y} of (G, 𝒜_G) read in 𝒜_{Kⁿ,y} and evaluated at y.
Equations
- AnalyticSpace.evalRestrict G y = (Manifold.eval K (AnalyticSpace.Kn K n) (AnalyticSpace.Kn K n) ↑y).comp (CommRingCat.Hom.hom ((AnalyticSpace.affine K n).restrictStalkIso ⋯ y).hom)
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evalRestrict of the germ of a section a of 𝒜_G over W ∋ y is the value a y.
The germs of the generators f j evaluate to 0 at a point of the support.
Evaluation of the fibre 𝒜_{G,y}/𝓘_y of the quotient sheaf at a point y of the support: the
value at y, well defined because 𝓘_y ⊆ 𝔪_y.
Equations
- One or more equations did not get rendered due to their size.
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The coordinate embedding ι_σ : K^{n−c} → Kⁿ is analytic.
Membership in the image of an open of the subtype U under the inclusion.
The underlying continuous map G' → V as a morphism of TopCat.
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The open Ω'' ⊆ K^{n−c} under an open Ω of V: the image in K^{n−c} of Ψ₀⁻¹ Ω ⊆ G'.
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The point of the open ι_V(Ω) ⊆ S under v ∈ Ω''.
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The function on K^{n−c} obtained by evaluating a germ family s over Ω ⊆ V along Ψ₀
(and 0 outside Ω'').
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The open of K^{n−c} under an open T ⊆ S of the local model: the points v ∈ G' with
Ψ₀ v ∈ T.
Equations
- D.pullOpensS T = ⋯.functor.obj ((TopologicalSpace.Opens.map (CategoryTheory.CategoryStruct.comp D.Ψtop D.V.inclusion')).obj T)
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The local formula: where the germ family s is the class of a section a of 𝒜_G, the
evaluated function is a ∘ Θ.
The evaluated function F s is analytic on Ω'': near each point it is a ∘ Θ for a section
a representing s, and Θ is analytic on G'.
The section of 𝒜_{K^{n−c}} over Ω'' obtained from a germ family s over Ω.
Equations
- D.secOf Ω s = Manifold.sectionOfContMDiffOn (D.Fsec Ω s) (D.pullOpens Ω) ⋯
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Compatibility with restriction.
The component of the sheaf map at Ω: evaluation of germ families along Ψ₀, a ring
homomorphism 𝒪_{X|V}(Ω) →+* 𝒜_{K^{n−c}}(Ω'').
Equations
- D.secRingHom Ω = { toFun := D.secOf Ω, map_one' := ⋯, map_mul' := ⋯, map_zero' := ⋯, map_add' := ⋯ }
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The component at Ω as a morphism of CommRingCat.
Equations
- D.ΨcApp Ω = CommRingCat.ofHom (D.secRingHom Ω)
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The sheaf component 𝒪_{X|V} ⟶ Ψ₀_* 𝒜_{G'}.
Equations
- D.Ψc = { app := fun (Ω : (TopologicalSpace.Opens ↑↑((AnalyticSpace.localModel K n G f).restrictOpen D.V).toPresheafedSpace)ᵒᵖ) => D.ΨcApp (Opposite.unop Ω), naturality := ⋯ }
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The morphism of presheafed spaces and its stalk maps #
The morphism of presheafed spaces (G', 𝒜_{G'}) → X|V: Ψ₀ on points, evaluation of germ
families along Ψ₀ on sections.
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The stalk map of ΨHom on the germ of a section s: the germ of the evaluated section.
The stalks of X|V are regular of dimension n − c #
The germs of the hs i at a point of V lie in the maximal ideal (the hs vanish on the
support).
The germs of the hs i at a point of V have independent differentials.
The stalk ideal 𝓘_y of the local model, transported to 𝒜_{Kⁿ,y} along restrictStalkIso,
is the ideal generated by the germs of the f j.
The stalk of the local model at a point w of V, read in 𝒜_{Kⁿ,w}:
𝒪_{X,w} ≅ 𝒜_{Kⁿ,w}/(hs).
Equations
- One or more equations did not get rendered due to their size.
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The algebraic heart of Hironaka's statement [Hir64, Ch. 0, §1, p. 121]: the stalks of X|V
are regular local rings of dimension n − c.
Injectivity of the stalk maps: the dimension argument #
A surjective stalk map of ΨHom is injective: its source 𝒪_{X|V, Ψ₀ v} is a regular local
domain of dimension n − c (isRegularLocalRing_stalk_restrict), its target 𝒜_{K^{n−c}, v} has
the same dimension, and a proper ideal of a Noetherian local domain with a quotient of full
dimension is zero (Ideal.eq_bot_of_ringKrullDim_quotient_eq,
Hironaka/Algebra/Local/QuotientParameters.lean).
Surjectivity of the stalk maps: pulling germs back along π_σ ∘ e #
The projection π : Kⁿ → K^{n−c}, y ↦ π_σ(e y) (junk outside e.source).
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π = π_σ ∘ e is analytic on e.source.
The open Wg ⊆ Kⁿ on which the pullback g ∘ π of a section g of 𝒜_{G'} over Ω₀ is
analytic: e.source ∩ π⁻¹(Ω₀).
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The pullback g ∘ π as a section of 𝒜_{Kⁿ} over pullOpen Ω₀.
Equations
- D.pullSection Ω₀ g = Manifold.sectionOfContMDiffOn (Manifold.extendSection K (AnalyticSpace.Kn K (n - c)) g ∘ D.π) (D.pullOpen Ω₀) ⋯
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The trace of pullOpen Ω₀ on G.
Equations
- D.pullOpenG Ω₀ = (TopologicalSpace.Opens.map G.inclusion').obj (D.pullOpen Ω₀)
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The pullback as a section of 𝒜_G.
Equations
- D.pullSectionG Ω₀ g = (CategoryTheory.ConcreteCategory.hom ((AnalyticSpace.affine K n).presheaf.map (CategoryTheory.homOfLE ⋯).op)) (D.pullSection Ω₀ g)
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The germ family of the pullback on the support.
Equations
- One or more equations did not get rendered due to their size.
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The open of V over pullOpen Ω₀.
Equations
- One or more equations did not get rendered due to their size.
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The pullback germ family as a section of X|V over pullOpenV Ω₀.
Equations
- D.pullFamilyV Ω₀ g = (CategoryTheory.ConcreteCategory.hom ((AnalyticSpace.localModel K n G f).presheaf.map (CategoryTheory.homOfLE ⋯).op)) (D.pullFamily Ω₀ g)
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The evaluated pull-back family is the section g itself: (g ∘ π) ∘ Θ = g.
Surjectivity of the stalk maps: every germ g at v ∈ G' is the image of the germ family of
g ∘ π.
The K-isomorphism #
The morphism of locally ringed spaces (G', 𝒜_{G'}) ⟶ X|V.
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Ψ carries the constants to the constants: it is a K-morphism.
The K-morphism (G', 𝒜_{G'}) ⟶ X|V.
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The K-isomorphism X|V ≅ (G', 𝒜_{G'}) [Hir64, Ch. 0, §1, p. 121].
Equations
- D.kIso = (CategoryTheory.asIso D.Ψ).symm
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The implicit function theorem for a local model [Hir64, Ch. 0, §1, p. 121]: if at a point z of
the local model X = V(f₁, …, f_k) ⊆ G ⊆ Kⁿ the ideal 𝓘_z = (f₁, …, f_k)_z of 𝒜_{Kⁿ,z} is
generated by c germs h₁, …, h_c with linearly independent differentials at z, then a
neighbourhood X|V of z is K-isomorphic to (G', 𝒜_{G'}) for an open G' ⊆ Kⁿ⁻ᶜ.