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Hironaka.Manifold.FiniteSuccession.CompatibleFamily.Defs

Compatible families of finite successions over the compact subsets #

Włodarczyk's compatible-family form of principalization Wlo09, Theorem 2.0.3; Definition 3.2.6; Theorem 3.5.1 (2), the form in which Hironaka's Main Theorem II''(N) and the real-analytic principalization theorem are stated: a proper analytic map M̃ → M which over an open neighbourhood of every compact set is a finite composite of blow-ups with smooth centres, compatibly across compacts. Włodarczyk's principalization is "locally but not globally a sequence of blow-ups at smooth centers" [Wlo09, Introduction]: over a neighbourhood U of a compact set Z the morphism splits into a finite sequence of blow-ups U = U_0 ← U_1 ← ⋯ ← U_r with smooth centres C_{i-1} ⊆ U_{i-1}, and for Z_1 ⊆ Z_2 with U_1 ⊆ U_2 the restriction of the sequence over U_2 to U_1 "determines" the sequence over U_1 — it is an extension of it in the sense of [Wlo09, Definition 3.2.6]: the same blow-ups with isomorphisms (blow-ups with empty centre) interspersed.

The restriction of a finite succession to an open subset #

theorem AnalyticManifold.FiniteSuccession.contMDiff_codRestrictOpens {𝕜 : Type} [RCLike 𝕜] {E : Type u_1} [NormedAddCommGroup E] [NormedSpace 𝕜 E] {N M' : AnalyticManifold 𝕜 E} {f : N.carrier → M'.carrier} (hf : ContMDiff (modelWithCornersSelf 𝕜 E) (modelWithCornersSelf 𝕜 E) ⊤ f) {V : TopologicalSpace.Opens M'.carrier} {f' : N.carrier → ↥V} (hf' : ∀ (p : N.carrier), ↑(f' p) = f p) :

A map into an open subset V of a manifold M' is analytic when it is analytic as a map into M' (Mathlib's liftPropWithinAt_subtypeVal_comp_iff; the general-domain form of contMDiff_codRestrict_opens).

The trace of U₁ on the stage U_i of S: the preimage of U₁ under the composite blow-down σ^i : U_i → U₂ ⊆ M (Włodarczyk's restriction of the factorization to Ũ₁, [Wlo09, Theorem 2.0.3 (4)]).

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    The later stages of the restriction: the traces of U₁ on U_1, …, U_r.

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      The restricted blow-downs σ_{i+1}| between the traces: the first lands in U₁ itself, the others between traces of later stages (a blowing-up restricted over an open subset).

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        def AnalyticManifold.FiniteSuccession.restrictOpensIncl {𝕜 : Type} [RCLike 𝕜] {E : Type u_1} [NormedAddCommGroup E] [NormedSpace 𝕜 E] {M : AnalyticManifold 𝕜 E} {U₂ U₁ : TopologicalSpace.Opens M.carrier} (h : U₁ ≤ U₂) :
        AnalyticMap (M.restrict U₁) (M.restrict U₂)

        The open inclusion U₁ → U₂ as an analytic map (Mathlib's Opens.inclusion with contMDiff_inclusion), the stage-0 inclusion of the restriction.

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          noncomputable def AnalyticManifold.FiniteSuccession.restrictOpensCenterAux {𝕜 : Type} [RCLike 𝕜] {E : Type u_1} [NormedAddCommGroup E] [NormedSpace 𝕜 E] {M : AnalyticManifold 𝕜 E} {U₂ : TopologicalSpace.Opens M.carrier} (S : (M.restrict U₂).FiniteSuccession) {U₁ : TopologicalSpace.Opens M.carrier} (h : U₁ ≤ U₂) (i : ℕ) (hi : i < S.length) :

          The restricted centres C_i ∩ σ^{-i}(U₁): the centre C_i comapped along the inclusion of the trace (possibly empty: Włodarczyk's isomorphism steps, [Wlo09, Definition 3.2.6, Remark (1)]).

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            The trace of U₁ in U₂, as an open of the stage U_0 = U₂, is U₁: the canonical analytic isomorphism ↥(val⁻¹' U₁) ≃ ↥U₁ (the stage-0 transport).

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              The inverse of the stage-0 transport as an analytic map U₁ → ↥(val⁻¹' U₁).

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                Each restricted map is the monoidal transformation of the restricted centre: a blowing-up restricted over an open subset is the blowing-up of the restricted centre (IsBlowUp.restrictOpens'), with the trace lemmas for closed submanifolds and their ideal sheaves (IsClosedSubmanifold.preimage_val, isIdealSheafOf_pullback_val); at stage 0 the statement is transported along restrictTraceDiffeomorph (IsBlowUp.diffeomorph_comp, IsClosedSubmanifold.preimage_of_isLocalDiffeomorph, comap_idealSheaf_of_isLocalDiffeomorph).

                noncomputable def AnalyticManifold.FiniteSuccession.restrict {𝕜 : Type} [RCLike 𝕜] {E : Type u_1} [NormedAddCommGroup E] [NormedSpace 𝕜 E] {M : AnalyticManifold 𝕜 E} {U₂ : TopologicalSpace.Opens M.carrier} (S : (M.restrict U₂).FiniteSuccession) {U₁ : TopologicalSpace.Opens M.carrier} (h : U₁ ≤ U₂) :

                The restriction of a finite succession S over the open U₂ ⊆ M to an open U₁ ≤ U₂ (Włodarczyk's restriction of the factorization of prin_{I|Ũ_2} to Ũ_1, [Wlo09, Theorem 2.0.3 (4)]): the stages are the preimages (σ^i)⁻¹(U₁) ⊆ U_i, the centres the restrictions C_i ∩ (σ^i)⁻¹(U₁) (possibly empty: Włodarczyk's isomorphism steps, [Wlo09, Definition 3.2.6, Remark (1)]), the maps the restrictions of the σ_{i+1} — a blow-up restricted to an open subset is the blow-up of the open subset with the restricted centre, as is immediate from the chart description of the blowing-up [BM88, Definition 4.1] (IsBlowUp.restrictOpens').

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                  Włodarczyk's extension relation #

                  def AnalyticManifold.FiniteSuccession.stageMapLE {𝕜 : Type} [RCLike 𝕜] {E : Type u_1} [NormedAddCommGroup E] [NormedSpace 𝕜 E] {M : AnalyticManifold 𝕜 E} (S : M.FiniteSuccession) {a b : Fin (S.length + 1)} (hab : a ≤ b) :
                  AnalyticMap (S.stage b) (S.stage a)

                  The composite σ_{a+1} ∘ ⋯ ∘ σ_b : U_b → U_a of the maps of S between two stages a ≤ b (Nat.leRecOn on a ≤ b; the identity at a = b, σ_{a+1} at b = a + 1; stageMap is the case a = 0).

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                    def AnalyticManifold.FiniteSuccession.centerAt {𝕜 : Type} [RCLike 𝕜] {E : Type u_1} [NormedAddCommGroup E] [NormedSpace 𝕜 E] {M : AnalyticManifold 𝕜 E} (S : M.FiniteSuccession) (a : Fin (S.length + 1)) (ha : ↑a < S.length) :

                    The centre C_a on the stage U_a, a < r, indexed by the stage.

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                      Włodarczyk's extension of a sequence of blow-ups [Wlo09, Definition 3.2.6]: T is an extension of S when T is a sequence of blow-ups and isomorphisms M = T_0 = ⋯ = T_{j_1-1} ← T_{j_1} = ⋯ = T_{j_2-1} ← ⋯ ← T_{j_m} = ⋯ = T_{m'} with T_{j_i} = S_i: there are indices j_1 < ⋯ < j_m (m = S.length, m' = T.length) such that the blow-ups of T at the indices j_i are those of S (the stages T_{j_i} identified with S_i over M, compatibly with the maps and the centres) and every other step of T is an isomorphism, a blow-up with empty centre. In the Lean: a block index blk : {0, …, m'} → {0, …, m} (the stage T_k is identified with S_{blk k}; blk 0 = 0, blk m' = m, each step raises blk by 0 or 1, the steps raising it being the j_i), identifications e k : T_k ≃ S_{blk k} (Włodarczyk's "=": analytic isomorphisms over M, i.e. commuting with the composite blow-downs, so that e 0 is the identity of M), compatible with the maps (σ^S_{blk k + 1} ∘ ⋯ ∘ σ^S_{blk (k+1)} ∘ e (k+1) = e k ∘ σ^T_{k+1}, through stageMapLE: at a jump the blow-up of S, at a non-jump the identity) and with the centres (at a jump C^T_k is the pull-back of C^S_{blk k} along e k); at a non-jump the step is an isomorphism, a blow-up with empty centre [Wlo09, Definition 3.2.6, Remark (1)]. "The definition of extension arises naturally when we pass to open subsets of the considered ambient manifold" (loc. cit.); [Wlo09, Theorem 3.5.1 (2)] states the compatibility of the canonical resolution with local analytic isomorphisms in these terms. That the restriction of a compatible family's succession is an extension of the succession over the smaller compact is the content of ExtensionCompatibleFamily's last field, not of this definition.

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                        A morphism of finite successions over φ : N → M, from the finite succession R over an open U' of N to the finite succession S over an open U of M. With r = S.length and r' = R.length: an index j_k = blk k of a stage of R for every stage S_k, with j_0 = 0, j_r = r' and each step of S raising the index by 0 or 1, and analytic maps f_k : R_{j_k} → S_k (map k) lying over φ (σ^S_k ∘ f_k = φ ∘ σ^R_{j_k}, read in M through the inclusions of U and U') and compatible with the blow-downs (σ^S_{k+1} ∘ f_{k+1} = f_k ∘ σ^R_{j_k + 1} ∘ ⋯ ∘ σ^R_{j_{k+1}}, through stageMapLE). The pull-back and the push-forward of successions (IsPullbackUpToEmptyAlong, IsPushforwardUpToEmptyAlong) are morphisms with conditions on the maps and the centres.

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                          R, a finite succession over an open U' of N, is the pull-back of the finite succession S over an open U of M along g : N → M, up to blow-ups with empty centre: there is a morphism R → S over g (FiniteSuccession.Hom), with index j_k and maps f_k : R_{j_k} → S_k, whose maps are local analytic isomorphisms, such that at a step raising the index the centre of R is the pull-back f_k^*(C_k) of the centre of S and at a step that does not, the pull-back of the centre is empty. So R is the sequence of the fibre products N ×_M S_k with some of its blow-ups of empty centre (isomorphisms) removed.

                          Relation to the source.

                          • Translation. R.IsPullbackUpToEmptyAlong S g is Włodarczyk's "the induced resolution $\varphi^*(M_{iZ_i})$ is an extension of the canonical resolution of $\varphi^*(M_Z, I, E, \mu)$" [Wlo09, Theorem 3.5.1 (2)], read for successions: the induced sequence $g^*(S)$, of the fibre products $N \times_M S_k$ Wlo09, Proposition 3.4.1; Definition 3.4.2, is an extension of $R$ in the sense of [Wlo09, Definition 3.2.6] (FiniteSuccession.IsExtensionOf).
                          • Restatement. The fibre products $N \times_M S_k$ are not formed. The relation is stated through local analytic isomorphisms $f_k$ from the stages of $R$ to those of $S$, lying over $g$ (Włodarczyk's lifts $\varphi_k$ of [Wlo09, Proposition 3.4.1 (1)], read on the stages of $R$), compatible with the blow-downs, with the centre of $R$ the pulled-back centre at a step that raises the index and an empty pulled-back centre at the others. These data determine the stages of $R$ as the fibre products, because a blowing-up commutes with pull-back along a local analytic isomorphism and $f_0$ is the restriction of $g$.
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                            S, a finite succession over an open U of M, is the push-forward of the finite succession R over an open U' of N along the closed embedding τ : N → M, up to blow-ups whose centres lie outside the part over τ(U') — Kollár's j_* B [Kol07, Definition 30.3], with centres Z_i^X := (j_i)_*(Z_i^S) and the natural inclusions j_i : S_i → X_i of the strict transforms of τ(N), for a succession S over an open U ⊇ τ(U'): there is a morphism R → S over τ (FiniteSuccession.Hom), with index j_k and maps f_k : R_{j_k} → S_k, whose maps are embeddings with image closed in the part of S_k over τ(U'), such that at a step raising the index the centre of R is the preimage f_k⁻¹(C_k) of the centre of S, at a step that does not, f_k misses the centre, and every point of a centre of S lying over τ(U') is in the image of f_k. So over τ(U') the centres of S are the images of the centres of R and the images of the f_k are the strict transforms of τ(U'), and S is the push-forward of R with blow-ups whose centres lie away from τ(U') interspersed.

                            Relation to the source.

                            • Translation. S.IsPushforwardUpToEmptyAlong R τ is Kollár's equation $B(X, I_X, E) = j_* B(Y, I_Y, E|_Y)$ for a closed embedding $j$ [Kol07, 34.3], read over the opens of two compatible families: $j_* B$ is the push-forward of [Kol07, Definition 30.3], whose centres are $Z_i^X := (j_i)_*(Z_i^S)$ for the natural inclusions $j_i \colon S_i \to X_i$ of the strict transforms.
                            • Restatement. Kollár's equation compares sequences over one space. Here the succession over the open $U$ of $M$ is compared with the succession over an open $U'$ of $N$ with $\tau(U') \subseteq U$, so it is the push-forward up to the blow-ups whose centres lie outside the part over $\tau(U')$ — the blow-ups of the sequence over $\tau^{-1}(U)$ that the sequence over the smaller open $U'$ omits, as the pull-back relation IsPullbackUpToEmptyAlong omits the blow-ups with empty pulled-back centre.
                            • Restatement. The strict transforms $S_i$ and the inclusions $j_i$ are not formed. The relation is stated through embeddings $f_k$ from the stages of $R$, whose images are closed in the part over $\tau(U')$ and contain every centre point over $\tau(U')$, with the centre of $R$ the preimage of the centre of $S$ at a step raising the index and $f_k$ missing the centre at the others. These data determine $S$ over $\tau(U')$ as the push-forward: $f_0$ is the restriction of $\tau$, and the image of $f_{k+1}$ is the strict transform of the image of $f_k$ under a blow-up whose centre is the image of a centre of $R$, or misses the image.
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                              Compatible families of finite successions over the compact subsets #

                              structure AnalyticManifold.ExtensionCompatibleFamily {𝕜 : Type} [RCLike 𝕜] {E : Type u_1} [NormedAddCommGroup E] [NormedSpace 𝕜 E] (M : AnalyticManifold 𝕜 E) :
                              Type (max (u + 1) u_1)

                              Włodarczyk's data in [Wlo09, Theorem 2.0.3 (1), (4)] with [Wlo09, Definition 3.2.6], the compatible-family form of the analytic main theorems: a manifold M̃ (space) with an analytic map M̃ → M (map; Włodarczyk's prin_I, Hironaka's canonical modification X_γ → X); for every compact K ⊆ M an open neighbourhood U_K = nhd K ⊇ K, monotone in K ("corresponding open neighborhoods U_1 ⊂ U_2"), and a finite succession seq K of blow-ups with smooth centres over U_K whose end result U_r is identified with Ũ = map⁻¹(U_K) over U_K (toSpace, map_toSpace, toSpace_isIso: "U_r = Ũ", "the restriction prin_{I|Ũ} splits into" the sequence); and the compatibility (4): for K_1 ⊆ K_2 the restriction of seq K_2 to U_{K_1} is an extension of seq K_1 — "the restriction of the factorization of prin_{I|Ũ_2} to Ũ_1 determines the factorization of prin_{I|Ũ_1}". The properness of map is a clause of the main theorems.

                              Relation to the source.

                              • Restatement. The compatibility of the identifications across compacts (over $U_{K_1}$, toSpace K_2 restricted to the end result of the restriction of seq K_2 is toSpace K_1 after the identification of the end results given by the extension) is not a field because it is a theorem, ExtensionCompatibleFamily.toSpace_comp_restrictStageIncl_eq (Hironaka.Resolution.Analytic.Wlo09.FamilyCoherence): a map from the end result of a succession over $U_K$ to $\tilde M$ over $U_K$ is unique (ExtensionCompatibleFamily.eq_of_map_comp_eq).
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                                The compatible family F' over N is the pull-back of the compatible family F over M along g : N → M: for compacts K' ⊆ N, K ⊆ M with g(U_{K'}) ⊆ U_K, the succession of F' over U_{K'} is the pull-back along g of the succession of F over U_K, up to blow-ups with empty centre (FiniteSuccession.IsPullbackUpToEmptyAlong, [Wlo09, Theorem 3.5.1 (2)]).

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                                  The compatible family F over M is the push-forward of the compatible family F' over N along τ : N → M: for compacts K' ⊆ N, K ⊆ M with τ(U_{K'}) ⊆ U_K, the succession of F over U_K is the push-forward along τ of the succession of F' over U_{K'}, up to blow-ups whose centres lie outside the part over τ(U_{K'}) (FiniteSuccession.IsPushforwardUpToEmptyAlong, [Kol07, 34.3]).

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