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Hironaka.Resolution.Analytic.Kol07Thm45.PieceIndependence

Padded embeddings, shears, the transport of an embedding along an isomorphism, and the local #

resolution map over the piece

Two closed embeddings i₁ : X ↪ 𝕜ⁿ, i₂ : X ↪ 𝕜ᵐ become equivalent under an analytic automorphism of 𝕜ⁿ⁺ᵐ after the coordinate inclusions: extend i₁, i₂ (locally) to j₁, j₂, shear by (x, y) ↦ (x, y + j₂(x)), shear by (x, y) ↦ (x + j₁(y), y), compose [Kol07, Lemma 39]; Włodarczyk's Lemma 4.8.1 is the same statement, with two explicit automorphisms of the doubled affine space [Wlo05, Lemma 4.8.1]. The ambient dimension may be increased at any time by 𝕜ⁿ ↪ 𝕜ⁿ⁺ᵐ [Kol07, Theorem 36, proof], as in Włodarczyk's passage to a common ambient dimension [Wlo09, §7.1]. The algebraic counterparts are shearX, shearY, prodEmb and coordInclFst of Hironaka/Resolution/Algebraic/Kol07/Thm36/AffineSpace.lean. This module constructs the analytic terms:

Conventions: the one-piece ambient pieceAmbient 𝕜 G; the linear chart of 𝕜ⁿ is the identity (ContinuousLinearEquiv.refl). The map localResolutionToPiece lands in the piece itself rather than in the open subspace X | embPreimage E W, so that its compositions with the transitions between pieces take place in one space; the open subspace is reached by restricting along the open set embPreimage E W (Hom.restrictSet). Not in the sources beyond the items cited; bookkeeping.

The padding of a nonzero ideal is nonzero, for every σ #

The padding of an ideal nonzero at every stalk is nonzero at every stalk, for every embedding of coordinates σ — off the slice the padded ideal is the unit ideal, on the slice (p^*J + 𝓘_S)_{s w} = (s^*)⁻¹ J_w contains p^* J_w, and s^* ∘ p^* = id.

The shears (x, y) ↦ (x, y + j x) and (x, y) ↦ (x + j y, y) #

theorem Hironaka.Manifold.contDiff_append_zero_left {𝕜 : Type} [RCLike 𝕜] {n m : ℕ} :
ContDiff 𝕜 ⊤ fun (b : Fin m → 𝕜) => Fin.append 0 b

The block inclusion b ↦ (0, b) of 𝕜ᵐ into 𝕜ⁿ⁺ᵐ is analytic.

theorem Hironaka.Manifold.contDiff_append_zero_right {𝕜 : Type} [RCLike 𝕜] {n m : ℕ} :
ContDiff 𝕜 ⊤ fun (a : Fin n → 𝕜) => Fin.append a 0

The block inclusion a ↦ (a, 0) of 𝕜ⁿ into 𝕜ⁿ⁺ᵐ is analytic.

theorem Hironaka.Manifold.contDiff_comp_castAdd {𝕜 : Type} [RCLike 𝕜] {n m : ℕ} :
ContDiff 𝕜 ⊤ fun (z : Fin (n + m) → 𝕜) => z ∘ Fin.castAdd m

The projection z ↦ z ∘ castAdd m onto the first block is analytic.

theorem Hironaka.Manifold.contDiff_comp_natAdd {𝕜 : Type} [RCLike 𝕜] {n m : ℕ} :
ContDiff 𝕜 ⊤ fun (z : Fin (n + m) → 𝕜) => z ∘ Fin.natAdd n

The projection z ↦ z ∘ natAdd n onto the second block is analytic.

theorem Hironaka.Manifold.append_zero_left_comp_castAdd {𝕜 : Type} [RCLike 𝕜] {n m : ℕ} (b : Fin m → 𝕜) :

The first block of (0, b) is 0.

theorem Hironaka.Manifold.append_zero_right_comp_natAdd {𝕜 : Type} [RCLike 𝕜] {n m : ℕ} (a : Fin n → 𝕜) :

The second block of (a, 0) is 0.

def Hironaka.Manifold.shearSnd {𝕜 : Type} [RCLike 𝕜] {n m : ℕ} (O : TopologicalSpace.Opens (Fin n → 𝕜)) (j : (Fin n → 𝕜) → Fin m → 𝕜) (hj : ContDiffOn 𝕜 ⊤ j ↑O) :
PartialDiffeomorph (modelWithCornersSelf 𝕜 (Fin (n + m) → 𝕜)) (modelWithCornersSelf 𝕜 (Fin (n + m) → 𝕜)) (Fin (n + m) → 𝕜) (Fin (n + m) → 𝕜) ⊤

The shear (x, y) ↦ (x, y + j(x)), an analytic automorphism of the cylinder O × 𝕜ᵐ ⊆ 𝕜ⁿ⁺ᵐ over an open O ⊆ 𝕜ⁿ on which j is analytic; its inverse is the shear by −j. It carries the coordinate inclusion x ↦ (x, 0) to the graph x ↦ (x, j(x)): the first automorphism of [Kol07, Lemma 39, proof] (compare the automorphisms of [Wlo05, Lemma 4.8.1]).

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    def Hironaka.Manifold.shearFst {𝕜 : Type} [RCLike 𝕜] {n m : ℕ} (O : TopologicalSpace.Opens (Fin m → 𝕜)) (j : (Fin m → 𝕜) → Fin n → 𝕜) (hj : ContDiffOn 𝕜 ⊤ j ↑O) :
    PartialDiffeomorph (modelWithCornersSelf 𝕜 (Fin (n + m) → 𝕜)) (modelWithCornersSelf 𝕜 (Fin (n + m) → 𝕜)) (Fin (n + m) → 𝕜) (Fin (n + m) → 𝕜) ⊤

    The shear (x, y) ↦ (x + j(y), y), an analytic automorphism of the cylinder 𝕜ⁿ × O ⊆ 𝕜ⁿ⁺ᵐ over an open O ⊆ 𝕜ᵐ on which j is analytic; its inverse is the shear by −j. It carries the coordinate inclusion y ↦ (0, y) to the graph y ↦ (j(y), y): the second automorphism of [Kol07, Lemma 39, proof] (compare the automorphisms of [Wlo05, Lemma 4.8.1]).

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      theorem Hironaka.Manifold.shearSnd_apply {𝕜 : Type} [RCLike 𝕜] {n m : ℕ} (O : TopologicalSpace.Opens (Fin n → 𝕜)) (j : (Fin n → 𝕜) → Fin m → 𝕜) (hj : ContDiffOn 𝕜 ⊤ j ↑O) (z : Fin (n + m) → 𝕜) :
      ↑(shearSnd O j hj).toPartialEquiv z = z + Fin.append 0 (j (z ∘ Fin.castAdd m))

      The value of the shear (x, y) ↦ (x, y + j(x)) (rfl).

      theorem Hironaka.Manifold.shearFst_apply {𝕜 : Type} [RCLike 𝕜] {n m : ℕ} (O : TopologicalSpace.Opens (Fin m → 𝕜)) (j : (Fin m → 𝕜) → Fin n → 𝕜) (hj : ContDiffOn 𝕜 ⊤ j ↑O) (z : Fin (n + m) → 𝕜) :
      ↑(shearFst O j hj).toPartialEquiv z = z + Fin.append (j (z ∘ Fin.natAdd n)) 0

      The value of the shear (x, y) ↦ (x + j(y), y) (rfl).

      The closed subspace along an analytic map with J' = f^* J #

      The compatibility Compat for Sp(f) when the source ideal IS the pull-back of the target one (comap_ofManifoldHom_eq_pullback, compat_comap). Any two models.

      noncomputable def Manifold.IdealSheaf.homOfPullbackEq {𝕜 : Type} [RCLike 𝕜] {k n : ℕ} {A : AnalyticManifold 𝕜 (Fin k → 𝕜)} {A' : AnalyticManifold 𝕜 (Fin n → 𝕜)} (f : A'.carrier → A.carrier) (hf : ContMDiff (modelWithCornersSelf 𝕜 (Fin n → 𝕜)) (modelWithCornersSelf 𝕜 (Fin k → 𝕜)) ⊤ f) {J' : A'.IdealSheaf} {J : A.IdealSheaf} (h : J' = pullback f hf J) :

      The morphism of closed subspaces over Sp(f) when J' = f^* J: quotientMap along Sp(f), for any analytic map between standard-model manifolds (two models allowed: 𝕜ⁿ → 𝕜ᵏ); restrictedIdealHom is its instance at an open inclusion.

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        The padded embeddings #

        noncomputable def Hironaka.Manifold.PieceEmbedding.padAlong {𝕜 : Type} [RCLike 𝕜] {n : ℕ} {X : AnalyticSpace 𝕜} {V : Set ↑↑X.toPresheafedSpace} (E : PieceEmbedding 𝕜 n X V) {n' : ℕ} (σ : Fin n ↪ Fin n') :
        PieceEmbedding 𝕜 n' X V

        The piece embedding padded along an embedding of coordinates σ : Fin n ↪ Fin n' — the ambient padOpens σ G, the ideal padIdeal σ 𝓘, the embedding X|V ≅ Sp(G)/𝓘 ≅ Sp(padOpens σ G)/padIdeal σ 𝓘 through the slice isomorphism of PadIdeal.lean (the enlargement of the ambient space in [Kol07, Theorem 36, proof]; the common ambient dimension of [Wlo09, §7.1]).

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          theorem Hironaka.Manifold.PieceEmbedding.padAlong_G {𝕜 : Type} [RCLike 𝕜] {n : ℕ} {X : AnalyticSpace 𝕜} {V : Set ↑↑X.toPresheafedSpace} (E : PieceEmbedding 𝕜 n X V) {n' : ℕ} (σ : Fin n ↪ Fin n') :
          (E.padAlong σ).G = padOpens σ E.G

          The ambient of the padded embedding is the padded open (rfl).

          theorem Hironaka.Manifold.PieceEmbedding.padAlong_ideal {𝕜 : Type} [RCLike 𝕜] {n : ℕ} {X : AnalyticSpace 𝕜} {V : Set ↑↑X.toPresheafedSpace} (E : PieceEmbedding 𝕜 n X V) {n' : ℕ} (σ : Fin n ↪ Fin n') :

          The ideal of the padded embedding is the padded ideal (rfl).

          noncomputable def Hironaka.Manifold.PieceEmbedding.padLeft {𝕜 : Type} [RCLike 𝕜] {n : ℕ} {X : AnalyticSpace 𝕜} {V : Set ↑↑X.toPresheafedSpace} (E : PieceEmbedding 𝕜 n X V) (m : ℕ) :
          PieceEmbedding 𝕜 (n + m) X V

          The left padding E.padLeft m : PieceEmbedding 𝕜 (n + m) X V — the coordinate inclusion x ↦ (x, 0) after E (the embedding i'_1 of [Kol07, Lemma 39]).

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            noncomputable def Hironaka.Manifold.PieceEmbedding.padRight {𝕜 : Type} [RCLike 𝕜] {n : ℕ} {X : AnalyticSpace 𝕜} {V : Set ↑↑X.toPresheafedSpace} (E : PieceEmbedding 𝕜 n X V) (m : ℕ) :
            PieceEmbedding 𝕜 (m + n) X V

            The right padding E.padRight m : PieceEmbedding 𝕜 (m + n) X V — the coordinate inclusion y ↦ (0, y) after E (the embedding i'_2 of [Kol07, Lemma 39]).

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              theorem Hironaka.Manifold.PieceEmbedding.padLeft_G {𝕜 : Type} [RCLike 𝕜] {n : ℕ} {X : AnalyticSpace 𝕜} {V : Set ↑↑X.toPresheafedSpace} (E : PieceEmbedding 𝕜 n X V) (m : ℕ) :

              The ambient of the left padding, G × 𝕜ᵐ as padOpens (castAddEmb m) G (rfl).

              theorem Hironaka.Manifold.PieceEmbedding.padRight_G {𝕜 : Type} [RCLike 𝕜] {n : ℕ} {X : AnalyticSpace 𝕜} {V : Set ↑↑X.toPresheafedSpace} (E : PieceEmbedding 𝕜 n X V) (m : ℕ) :

              The ambient of the right padding, 𝕜ᵐ × G as padOpens (natAddEmb m) G (rfl).

              The ambient point of an embedded point, and the points over an open #

              noncomputable def Hironaka.Manifold.PieceEmbedding.ambientPoint {𝕜 : Type} [RCLike 𝕜] {n : ℕ} {X : AnalyticSpace 𝕜} {V : Set ↑↑X.toPresheafedSpace} (E : PieceEmbedding 𝕜 n X V) (y : ↑↑(X.restrictSet V).toPresheafedSpace) :

              The ambient point i(y) ∈ G of a point y of the piece X|V: the image of y under the embedding followed by the closed-subspace inclusion Sp(G)/𝓘 → Sp(G).

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                The points of the piece over W — the points of X|V whose ambient point lies in the open W ⊆ G, the open subset of the piece over which the local resolution over W lives (the part of the germ Y_Z over W, [Wlo09, §4, (3)⇒(4)]); the image of localResolutionToPiece.

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                  The points over W form an open subset of the piece.

                  The transport of a piece embedding along an isomorphism of open subspaces #

                  noncomputable def Hironaka.Manifold.PieceEmbedding.transportAlongIso {𝕜 : Type} [RCLike 𝕜] {n : ℕ} {X : AnalyticSpace 𝕜} {V : Set ↑↑X.toPresheafedSpace} {Y : AnalyticSpace 𝕜} {U : Set ↑↑Y.toPresheafedSpace} (E : PieceEmbedding 𝕜 n Y U) (h : X.restrictSet V ⟶ Y.restrictSet U) (hh : CategoryTheory.IsIso h) :
                  PieceEmbedding 𝕜 n X V

                  The transport of a piece embedding along an isomorphism h : X|V ≅ Y|U: the same ambient G, the same ideal 𝓘, the embedding E.emb ∘ h. The analytic form, for an isomorphism of open subspaces, of the compatible embeddings of [Kol07, Lemma 41]: the ambient and the ideal are unchanged.

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                    theorem Hironaka.Manifold.PieceEmbedding.transportAlongIso_G {𝕜 : Type} [RCLike 𝕜] {n : ℕ} {X : AnalyticSpace 𝕜} {V : Set ↑↑X.toPresheafedSpace} {Y : AnalyticSpace 𝕜} {U : Set ↑↑Y.toPresheafedSpace} (E : PieceEmbedding 𝕜 n Y U) (h : X.restrictSet V ⟶ Y.restrictSet U) (hh : CategoryTheory.IsIso h) :
                    (E.transportAlongIso h hh).G = E.G

                    The transport keeps the ambient open (rfl).

                    theorem Hironaka.Manifold.PieceEmbedding.transportAlongIso_ideal {𝕜 : Type} [RCLike 𝕜] {n : ℕ} {X : AnalyticSpace 𝕜} {V : Set ↑↑X.toPresheafedSpace} {Y : AnalyticSpace 𝕜} {U : Set ↑↑Y.toPresheafedSpace} (E : PieceEmbedding 𝕜 n Y U) (h : X.restrictSet V ⟶ Y.restrictSet U) (hh : CategoryTheory.IsIso h) :

                    The transport keeps the ideal sheaf (rfl).

                    The transport's embedding is the composite E.emb ∘ h (rfl).

                    theorem Hironaka.Manifold.PieceEmbedding.ambientPoint_transportAlongIso {𝕜 : Type} [RCLike 𝕜] {n : ℕ} {X : AnalyticSpace 𝕜} {V : Set ↑↑X.toPresheafedSpace} {Y : AnalyticSpace 𝕜} {U : Set ↑↑Y.toPresheafedSpace} (E : PieceEmbedding 𝕜 n Y U) (h : X.restrictSet V ⟶ Y.restrictSet U) (hh : CategoryTheory.IsIso h) (x : ↑↑(X.restrictSet V).toPresheafedSpace) :

                    The ambient points correspond along h (rfl).

                    The local resolution map over the piece #

                    The restriction-of-a-quotient map Sp(W)/𝓘|W ⟶ Sp(G)/𝓘 along Sp(W ↪ G): the morphism of closed subspaces homOfPullbackEq at the open inclusion (the ideal 𝓘|W is the pullback of 𝓘 along the inclusion by definition, restrictOpens).

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                      noncomputable def Hironaka.Manifold.PieceEmbedding.localResolutionToPiece {𝕜 : Type} [RCLike 𝕜] {n : ℕ} {X : AnalyticSpace 𝕜} {V : Set ↑↑X.toPresheafedSpace} (E : PieceEmbedding 𝕜 n X V) (bed : BEDanFamStar 𝕜) (W : TopologicalSpace.Opens (pieceAmbient 𝕜 E.G).carrier) (hW : IsCompact (closure ↑W)) :

                      The local resolution map over the piece Ỹ → X|V — the local resolution map Π : Ỹ → Sp(W)/𝓘|W of PieceResolution.lean, followed by the restriction-of-a-quotient map Sp(W)/𝓘|W → Sp(G)/𝓘 and the inverse of the embedding X|V ≅ Sp(G)/𝓘: Włodarczyk's Ỹ_Z → Y_Z [Wlo09, §4, (3)⇒(4)], Kollár's resolution g : g⁻¹(X) → X [Kol07, Corollary 22, proof], which need not be a composite of smooth blow-ups [Kol07, Warning 23]. Its image lies in the open embPreimage E W of the piece (range_localResolutionToPiece_subset; over ℂ it is the closure of the simple points of Y ∩ W, as in the clause range Π = closure X.regularLocus of the resolution theorem — not all of the open over ℝ).

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                        The restriction-of-a-quotient map lies over Sp(W ↪ G): ι ∘ restrictedIdealHom = Sp(val) ∘ ι' on points.

                        The image of the local resolution map over the piece lies in the open embPreimage E W: every point of Ỹ maps to a point of the piece whose ambient point is in W.