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:
- The paddings.
PieceEmbedding.padAlong E σpads a piece embedding along an embedding of coordinatesσ : Fin n ↪ Fin n'with the tools ofPadIdeal.lean: the ambientpadOpens σ E.G, the idealpadIdeal σ E.ideal, the embeddingX|V ≅ Sp(G)/𝓘 ≅ Sp(padOpens σ G)/padIdeal σ 𝓘(the slice isomorphism inverted).padLeft E m(σ := Fin.castAddEmb m, the coordinate inclusionx ↦ (x, 0)) andpadRight E m(σ := Fin.natAddEmb m,y ↦ (0, y)) are the two paddings of Lemma 39.isNonzeroEverywhere_padIdeal_of_isNonzeroEverywhereis the nonvanishing of the padded ideal for an ARBITRARYσ(the padding of a nonzero ideal is nonzero, no padding coordinate needed), so that the paddings are total inm. - The shears.
shearSnd O j hj,shearFst O j hj: the analytic automorphisms(x, y) ↦ (x, y + j(x))ofO × 𝕜ᵐand(x, y) ↦ (x + j(y), y)of𝕜ⁿ × O, forjanalytic on the openO— Mathlib'sPartialDiffeomorphof the model space𝕜ⁿ⁺ᵐwith source and target the cylinder overO(the two automorphisms of [Kol07, Lemma 39, proof]; the local extensionsj₁, j₂are supplied where the two embeddings are compared, from the sheaf of germ families). - The transport.
PieceEmbedding.transportAlongIso E h hh: a piece embedding ofY|Ucomposed with an isomorphismX|V ≅ Y|Uis a piece embedding ofX|Vwith the SAME ambient and ideal — the analytic form, for an isomorphism of open subspaces, of the compatible embeddings of [Kol07, Lemma 41] (the projection argument of that lemma is not needed). - The composite.
PieceEmbedding.localResolutionToPiece E bed W hW: the local resolution mapΠ : Ỹ → Sp(W)/𝓘|W(PieceResolution.lean) followed by the restriction-of-a-quotient mapSp(W)/𝓘|W → Sp(G)/𝓘(the functoriality of the closed subspace alongSp(W ↪ G)) and the inverse of the embeddingX|V ≅ Sp(G)/𝓘— the mapỸ_Z → Y_Zof Włodarczyk's canonical desingularization [Wlo09, §4, (3)⇒(4)], landing in the pieceX|V, with image the openembPreimage E Wof the points ofX|Vwhose ambient point lies overW(ambientPoint).
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) #
The block inclusion b ↦ (0, b) of 𝕜ᵐ into 𝕜ⁿ⁺ᵐ is analytic.
The block inclusion a ↦ (a, 0) of 𝕜ⁿ into 𝕜ⁿ⁺ᵐ is analytic.
The first block of (0, b) is 0.
The second block of (a, 0) is 0.
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]).
Equations
- One or more equations did not get rendered due to their size.
Instances For
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]).
Equations
- One or more equations did not get rendered due to their size.
Instances For
The value of the shear (x, y) ↦ (x, y + j(x)) (rfl).
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.
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.
Equations
Instances For
The padded embeddings #
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]).
Equations
- One or more equations did not get rendered due to their size.
Instances For
The ambient of the padded embedding is the padded open (rfl).
The ideal of the padded embedding is the padded ideal (rfl).
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]).
Equations
- E.padLeft m = E.padAlong (Fin.castAddEmb m)
Instances For
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]).
Equations
- E.padRight m = E.padAlong (Fin.natAddEmb m)
Instances For
The ambient of the left padding, G × 𝕜ᵐ as padOpens (castAddEmb m) G (rfl).
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 #
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).
Equations
- E.ambientPoint y = ↑E.ideal.toAnalyticSpaceι (↑E.emb y)
Instances For
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.
Equations
- E.embPreimage W = {y : ↑↑(X.restrictSet V).toPresheafedSpace | E.ambientPoint y ∈ W}
Instances For
The points over W form an open subset of the piece.
The transport of a piece embedding along an isomorphism of open subspaces #
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.
Equations
- E.transportAlongIso h hh = { G := E.G, ideal := E.ideal, isNonzeroEverywhere := ⋯, isReduced := ⋯, emb := CategoryTheory.CategoryStruct.comp h E.emb, emb_isIso := ⋯ }
Instances For
The transport keeps the ambient open (rfl).
The transport keeps the ideal sheaf (rfl).
The transport's embedding is the composite E.emb ∘ h (rfl).
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).
Equations
- E.restrictedIdealHom W = Manifold.IdealSheaf.homOfPullbackEq ⇑((Hironaka.Manifold.pieceAmbient 𝕜 E.G).inclusion W) ⋯ ⋯
Instances For
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).
Equations
- One or more equations did not get rendered due to their size.
Instances For
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.