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Hironaka.Manifold.Resolution.Defs

The clauses of the analytic main theorems on a finite succession of monoidal transformations #

The clauses of Hironaka's Main Theorem II′(N) [Hir64, p. 156] on a finite succession of monoidal transformations U_0 ← U_1 ← ⋯ ← U_r of an analytic manifold (FiniteSuccession), in which the analytic principalization theorems state their conclusions over each compact set. They carry the names of the clauses of the algebraic Main Theorems II and II(N) and Corollary 1 on blow-up sequences of schemes, whose bodies they repeat with the manifold leaf predicates. One leaf predicate says more than its scheme namesake: the manifold IdealSheaf.IsSncBoundaryWith B D asserts simple normal crossings of B at every point and with D at the points of D, while the scheme IsSncBoundaryWith asserts the condition at the points of D only. So the first field of HasSncBoundaries here also asserts simple normal crossings of every intermediate boundary.

The clauses of Włodarczyk's locally finite embedded desingularization [Wlo09, Theorem 2.0.2] on the succession over each compact set are collected in one structure, named after the structure EmbeddedPair.IsDesingularizedBy of the algebraic embedded desingularization on blow-up sequences of schemes (the fields are named after the analytic notions they state):

The clauses of Włodarczyk's locally finite principalization [Wlo09, Theorem 2.0.3], whose value is a compatible family of finite successions over the compact sets (ExtensionCompatibleFamily), are collected in a structure on the family, named after Włodarczyk's term:

The functorial theorems assert the existence of an assignment of a compatible family to every input, with a property of each value and a functoriality package, as the algebraic functorial theorems assert a blow-up sequence functor (BlowUpSequenceFunctor); they differ in the inputs.

The boundaries E_i of the succession S started at B (S.boundarySeq B: E_0 = B and E_{i+1} = red(σ_{i+1}⁻¹(E_i) ∪ σ_{i+1}⁻¹(D_i))) have simple normal crossings with the centres, and the last one has simple normal crossings (Hir64, Main Theorem II′(N) (iii) and the first half of (iv), p. 156; [Wlo09, Theorem 2.0.3 (2)]).

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    The order of the weak transform J_i of J (S.weakTransformSeq J i) is a positive constant along the centre D_i, for every i ([Hir64, Main Theorem II′(N) (ii), p. 156]).

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      The closed subspace Y of M with ideal sheaf I is desingularized by the finite succession S : M = U_0 ← U_1 ← ⋯ ← U_r with composite σ : U_r → M [Wlo09, Theorem 2.0.2 (1)–(3), (6)]. With exceptional divisors E_i (the boundaries S.boundarySeq ⊤ i started at the empty boundary ⊤) and strict transforms Y_i of Y (S.strictTransformSubspaceSeq I i), Ỹ = Y_r: the centres C_i are smooth; every E_i has simple normal crossings with C_i and E_r has simple normal crossings; no point of a centre lies over a point of Reg(Y) (regularLocus); the support of E_r is the preimage of Sing(Y) = Y ∖ Reg(Y); Ỹ is smooth and has simple normal crossings with E_r; and σ^*(I_Y) = I_Ỹ · I_Ẽ with Ẽ a combination of the components of E_r. The analogue on manifolds of EmbeddedPair.IsDesingularizedBy on schemes.

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        The compatible family F is a locally finite principalization of the ideal sheaf I on M [Wlo09, Theorem 2.0.3 (1)–(3)]: with prin_I = F.map : M̃ → M, and over the neighbourhood U_K of a compact K ⊆ M the succession F.seq K : U_K = U_0 ← U_1 ← ⋯ ← U_r with composite σ_K : U_r → U_K and exceptional divisors E_i (the boundaries (F.seq K).boundarySeq ⊤ i started at the empty boundary ⊤): prin_I is proper; every U_K has compact closure; the centres C_i are smooth; every E_i has simple normal crossings with C_i and E_r has simple normal crossings; the total transform σ_K^*(I|_{U_K}) is, near every point, the ideal of an effective combination of the components of E_r through it; the total transform prin_I^*(I) on M̃ is a normal-crossings divisor; and prin_I is an isomorphism over the complement of the support of I. The compatibility of the successions over two compacts is a field of ExtensionCompatibleFamily. The analogue on manifolds of Triple.IsPrincipalizedBy on schemes, whose fields are Kollár's clauses (1)–(3) for a single blow-up sequence.

        Relation to the source.

        • Translation. I.IsLocallyFinitelyPrincipalizedBy F says that F is a locally finite principalization of $I$ in the sense of [Wlo09, Theorem 2.0.3]: F.map is $\mathrm{prin}_I \colon \tilde M \to M$; for a compact set $K$, F.nhd K is the open neighbourhood $U \supset K$ of Włodarczyk's clause (1) and F.seq K the factorization $(\ast)$ of $\mathrm{prin}_I$ over $U$, whose exceptional divisors $E_{U_i}$ are the boundaries (F.seq K).boundarySeq ⊤ i started at the empty boundary ⊤; his clause (4) is the compatibility of the family (ExtensionCompatibleFamily).
        • Translation. The fields are the clauses of [Wlo09, Theorem 2.0.3]: isProperMap the properness of $\mathrm{prin}_I$, isNonsingular_center the smooth centres of (1), hasSncBoundaries clause (2), and isMulBoundaryMonomial_pullback clause (3) over $U$, in which IsMulBoundaryMonomial J ⊤ B, with the unit ideal ⊤ as its first factor, says that $J$ is near every point the ideal of an effective combination of the hypersurfaces of the simple normal crossings family whose reduced ideal sheaf is $B$, here $E_{U_r}$; isNormalCrossingsDivisor_pullback is clause (3) for the total transform $\mathrm{prin}_I^*(I)$ on $\tilde M$.
        • Strengthening. The fields isCompact_closure_nhd and isIsoOver_compl_support have no counterpart among Włodarczyk's clauses.
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          The compatible family F is a locally finite embedded desingularization of the closed subspace Y of M with ideal sheaf I [Wlo09, Theorem 2.0.2]: with res_{Y,M} = F.map : M̃ → M, and over the neighbourhood U_K of a compact K ⊆ M the succession F.seq K, res_{Y,M} is proper, it is an isomorphism over the complement of the singular locus Sing(Y) = Y ∖ Reg(Y), every F.seq K desingularizes Y ∩ U_K (IsDesingularizedBy, clauses (1)–(3) and (6)), has no empty centre and has every centre of codimension at least two or of codimension one inside the exceptional divisor of its stage, and there are on M̃ an exceptional divisor E and a strict transform Ỹ gluing the last exceptional divisors and the last strict transforms of the successions: over every compact K, read on the last stage U_r of F.seq K through its identification toSpace K with res_{Y,M}⁻¹(U_K), E is E_r and Ỹ is the strict transform Y_r of Y ∩ U_K. Then E is the reduced ideal sheaf of a simple normal crossings family of hypersurfaces of M̃ with which Ỹ has simple normal crossings, transversally, and res_{Y,M}^*(I_Y) = I_Ỹ · I_Ẽ with Ẽ near every point an effective combination of the components of E. His clause (5), the compatibility of the successions over two compacts, is a field of ExtensionCompatibleFamily.

          Relation to the source.

          • Translation. I.IsLocallyFinitelyDesingularizedBy F says that F is the embedded desingularization of $Y$ in the sense of [Wlo09, Theorem 2.0.2]: F.map is $\mathrm{res}_{Y,M} \colon \tilde M \to M$, "proper bimeromorphic"; for a compact set $K$, F.nhd K is the open subset $U$ and F.seq K the factorization $(\ast)$ of $\mathrm{res}_{Y,M}$ over $U$, whose clauses (1)–(3) and (6) are IsDesingularizedBy; his clause (5) is the compatibility of the family (ExtensionCompatibleFamily).
          • Strengthening. isIsoOver_compl_sing, that $\mathrm{res}_{Y,M}$ is an isomorphism over $M \setminus \operatorname{Sing}(Y)$, says more than Włodarczyk's "bimeromorphic". Over $\operatorname{Reg}(Y)$ it follows from his clause (2); over $M \setminus Y$ it is not in [Wlo09, Theorem 2.0.2] but holds for his construction, an initial segment of the principalization of $I_Y$, which is an isomorphism over $M \setminus V(I_Y)$ [Wlo09, Lemma 4.0.3].
          • Translation. Włodarczyk's "divisor $E$" and "strict transform $\tilde Y$" on $\tilde M$ are the E and Y of exists_divisor_strictTransform. Its first clause identifies them over every compact with the $E_{U_r}$ and $\tilde Y \cap U_r$ of the factorization $(\ast)$: his "$\tilde Y$" and "$E$" name the global objects and their restrictions alike. Its other clauses are his clause (1) for $E$ and his clause (3) for the simple normal crossings of $\tilde Y$ with $E$, and his clause (6), $\sigma^*(I_Y) = I_{\tilde Y} I_{\tilde E}$ for $\sigma = \mathrm{res}_{Y,M}$, on $\tilde M$.
          • Restatement. The support of $E$, "the exceptional locus of $\mathrm{res}_{Y,M}$", and the smoothness of $\tilde Y$ in his clause (3) are read over every compact: through the first clause of exists_divisor_strictTransform they are the identity $|E_r| = \sigma_K^{-1}(\operatorname{Sing} Y)$ and the smoothness of $Y_r$ of IsDesingularizedBy, from which $|E| = \mathrm{res}_{Y,M}^{-1}(\operatorname{Sing} Y)$ and the smoothness of $\tilde Y$ follow (IsGloballyDesingularizedBy.support_eq, IsGloballyDesingularizedBy.isNonsingular).
          • Translation. center_ne_top reads the first half of Włodarczyk's Remark (2) after Theorem 2.0.3, that his centres are nonempty (the empty blow-up convention of [Kol07, 32]), and two_le_codim_or_boundarySeq_le_center reads its second half, that his centres have codimension at least two, together with his Remark (1): a centre of codimension one lies in the exceptional divisor, its blow-up is an isomorphism, and it stays a component of the exceptional divisor; the centres of codimension one are not removed from the successions.
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            The inputs of the functorial theorems #

            structure AnalyticManifold.IdealSheafPair (𝕜 : Type) [RCLike 𝕜] :
            Type (max (u + 1) (v + 1))

            A pair (M, I), the input of Włodarczyk's functorial principalization [Wlo09, Theorem 2.0.3]: an analytic manifold M over 𝕜, modelled on a finite-dimensional space E, with an ideal sheaf I on M with nonzero stalks (so on every connected component). Kollár's triple (X, I, ∅) [Kol07, Notation 64] with an empty boundary, on an analytic manifold; the model space is part of the input, so that one assignment covers the manifolds of every dimension.

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              class AnalyticManifold.HasUnderlyingManifold (C : Type w) (𝕜 : outParam Type) [RCLike 𝕜] :
              Type (max w (u + 1) (v + 1))

              A type C of inputs each with an underlying analytic manifold over 𝕜, modelled on a finite-dimensional space (the analogue of HasUnderlyingScheme for the algebraic inputs).

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                abbrev AnalyticManifold.CompatibleFamilyAssignment {𝕜 : Type} [RCLike 𝕜] (C : Type w) [HasUnderlyingManifold C 𝕜] :
                Type (max (max (u + 1) v) w)

                A compatible family assignment on the inputs C: a compatible family of finite successions of blow-ups (ExtensionCompatibleFamily) of the underlying manifold of every input — Włodarczyk's prin and res as rules on all pairs, the counterpart on manifolds of a blow-up sequence functor (BlowUpSequenceFunctor, [Kol07, Definition 31]). Its properties are the clauses of the functorial theorems.

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                  noncomputable abbrev AnalyticManifold.IdealSheafPair.pullback {𝕜 : Type} [RCLike 𝕜] (T : IdealSheafPair 𝕜) {N : AnalyticManifold 𝕜 T.E} (g : AnalyticMap N T.M) (hg : IsLocalDiffeomorph (modelWithCornersSelf 𝕜 T.E) (modelWithCornersSelf 𝕜 T.E) ⊤ ⇑g) :

                  The pull-back (N, g^*I) of the pair (M, I) along a local analytic isomorphism g : N → M of manifolds modelled on E: the source of the morphism of pairs over g [Wlo09, Theorem 3.5.1]. The pulled-back ideal sheaf has nonzero stalks (IdealSheaf.isNonzeroEverywhere_comap).

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                    structure AnalyticManifold.IdealSheaf.IsPushforwardAlong {𝕜 : Type} [RCLike 𝕜] {E : Type u_1} [NormedAddCommGroup E] [NormedSpace 𝕜 E] {E' : Type u_2} [NormedAddCommGroup E'] [NormedSpace 𝕜 E'] {M : AnalyticManifold 𝕜 E} {N : AnalyticManifold 𝕜 E'} (I : M.IdealSheaf) (J : N.IdealSheaf) (τ : ContMDiffMap (modelWithCornersSelf 𝕜 E') (modelWithCornersSelf 𝕜 E) N.carrier M.carrier ⊤) :

                    The ideal sheaf I on M is the push-forward of the ideal sheaf J on N along the closed embedding of analytic manifolds τ : N → M: τ is an analytic embedding (Mathlib's IsSmoothEmbedding at ω: an analytic immersion, of the form u ↦ (u, 0) in suitable charts near every point, which is a homeomorphism onto its image) with closed image, I contains the ideal of the closed submanifold τ(N) (the vanishing ideal vanishingStalk, stalk by stalk), and J = τ^*I. So the closed subspace of I lies in τ(N) and is the image of the closed subspace of J. The image τ(N) is a closed submanifold of M (IsClosedAnalyticEmbedding.exists_isClosedSubmanifold, for a finite-dimensional model) and N carries the analytic structure induced on it: every analytic map into M with values in τ(N) factors analytically through τ (IsClosedAnalyticEmbedding.exists_comp_eq).

                    Relation to the source.

                    • Translation. The embedding τ is Kollár's "closed embedding of smooth schemes" [Kol07, 34.3] for analytic manifolds, the embedding of Włodarczyk's "embeddings of ambient varieties" [Wlo09, Theorem 2.0.3]: $\tau$ identifies $N$ with the closed submanifold $\tau(N)$ of $M$, with its induced analytic structure.
                    • Translation. I.IsPushforwardAlong J τ is Kollár's hypothesis on the ideal sheaves in his commutation with closed embeddings [Kol07, 34.3]: "$j \colon Y \hookrightarrow X$ is a closed embedding of smooth schemes, $0 \neq I_Y \subset \mathcal{O}_Y$ and $0 \neq I_X \subset \mathcal{O}_X$ are ideal sheaves with $\mathcal{O}_X/I_X = j_*(\mathcal{O}_Y/I_Y)$", for an empty boundary — the quotient condition being the containment of the ideal sheaf of $\tau(N)$ in $I$ with $J = \tau^* I$; the nonzero stalks are conditions on the pairs. The containment is stated stalk by stalk, the stalks of the ideal sheaf of the submanifold $\tau(N)$ being the ideals of the germs vanishing on it.
                    • Translation. In Włodarczyk's notation, I.IsPushforwardAlong J τ says $I = \tau_*(J) \cdot \mathcal{O}_M$, the preimage of $\tau_*(J)$ under the surjection $\mathcal{O}_M \to \tau_*(\mathcal{O}_N)$ [Wlo09, Remark (3) after Theorem 2.0.3], the ideal for which the canonical resolution of $J$ with centres $C_i$ defines that of $I$, with the centres $\tau(C_i)$ [Wlo09, Theorem 3.5.1 (3)].
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                      The functoriality of an assignment on pairs #

                      A compatible family assignment P on the pairs (M, I) commutes with local analytic isomorphisms, in two forms. Over every pair of compact sets: for a local analytic isomorphism g : N → M of manifolds modelled on one space, the family P(N, g^*I) is the pull-back of P(M, I) along g (ExtensionCompatibleFamily.IsPullbackAlong): for compacts K' ⊆ N, K ⊆ M with g(U_{K'}) ⊆ U_K, the succession of P(N, g^*I) over U_{K'} is the pull-back along g of the succession of P(M, I) over U_K, up to blow-ups with empty centre. Globally: writing prin_I : M̃ → M and prin_J : Ñ → N for the maps of P(M, I) and P(N, J), J = g^*I, there is an analytic map g̃ : Ñ → M̃ over g (prin_I ∘ g̃ = g ∘ prin_J) which is a local analytic isomorphism, maps the fibre of prin_J over every y ∈ N bijectively onto the fibre of prin_I over g y, and is the only continuous map Ñ → M̃ over g; the fibre bijection with the local isomorphism is the identification of Ñ with the fibre product N ×_M M̃, stated without forming it.

                      Relation to the source.

                      • Translation. The structure is the last sentence of [Wlo09, Theorem 2.0.3], "the morphism $\mathrm{prin} \colon (\tilde M, \tilde I) \to (M, I)$ commutes with local analytic isomorphisms". isPullbackAlong is its form of [Wlo09, Theorem 3.5.1 (2)]: for a local analytic isomorphism $\varphi$, the sequence induced by $\varphi$ from the sequence of $I$ is an extension of the sequence of $\varphi^*(I)$. exists_lift is its global form, the "natural lifting" $\tilde\varphi$, "a local analytic isomorphism", of [Wlo09, Theorem 2.0.1 (3)]; the uniqueness makes the lift of a composite the composite of the lifts.
                      • Restatement. The identification of $\tilde N$ with $N \times_M \tilde M$ of [Wlo09, Proposition 3.4.1] is stated pointwise, as the bijection of $\tilde g$ between the fibres over corresponding points; over an open set on which $g$ is injective the lift is then an analytic isomorphism between the preimages.
                      • Interpretation. The exact equality of [Wlo09, Theorem 3.5.1 (1)] for a surjective local analytic isomorphism has no counterpart per pair of compact sets: for $g$ the identity and compacts $K' \subsetneq K$ with a centre of the succession over $U_K$ lying over $U_K \setminus U_{K'}$, the induced succession over $U_{K'}$ has an empty centre that the succession over $U_{K'}$ omits. Its global content is read as: for surjective $g$ the lift $\tilde g$ is a surjective local analytic isomorphism identifying $\tilde N$ with $N \times_M \tilde M$.
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                        A compatible family assignment P on the pairs (M, I) commutes with closed embeddings: for pairs (M, I) and (N, J) and a closed embedding of analytic manifolds τ : N → M along which I is the push-forward of J (IdealSheaf.IsPushforwardAlong: τ(N) a closed submanifold, I ⊇ 𝓘_{τ(N)}, J = τ^*I), the family P(M, I) is the push-forward of P(N, J) along τ (ExtensionCompatibleFamily.IsPushforwardAlong): for compacts K' ⊆ N, K ⊆ M with τ(U_{K'}) ⊆ U_K, the succession of P(M, I) over U_K is the push-forward along τ of the succession of P(N, J) over U_{K'}, up to blow-ups whose centres lie outside the part over τ(U_{K'}).

                        Relation to the source.

                        • Translation. CommutesWithClosedEmbeddings P is the rest of the last sentence of [Wlo09, Theorem 2.0.3], "the morphism $\mathrm{prin}$ commutes with … embeddings of ambient varieties", read as Kollár's commutation with closed embeddings [Kol07, Theorem 35 (5)] in the form of [Kol07, 34.3], $B(X, I_X, E) = j_* B(Y, I_Y, E|_Y)$ for an empty $E$.
                        • Restatement. Kollár's equation of blow-up sequences is stated over every pair of compact sets, up to blow-ups whose centres lie outside the part over $\tau(U_{K'})$, as the commutation with local analytic isomorphisms is: the succession over $U_K$ also blows up centres over $U_K \setminus \tau(U_{K'})$, which the succession over $U_{K'}$ does not see.
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                          Embedded pairs #

                          structure AnalyticManifold.EmbeddedPair (𝕜 : Type) [RCLike 𝕜] :
                          Type (max (u + 1) (v + 1))

                          An embedded pair (M, Y), the input of Włodarczyk's locally finite embedded desingularization [Wlo09, Theorem 2.0.2]: an analytic manifold M over 𝕜, modelled on a finite-dimensional space E, with a reduced closed analytic subspace Y ⊆ M, given by its ideal sheaf (every stalk radical). The analogue on manifolds of the algebraic AlgebraicGeometry.EmbeddedPair of Włodarczyk's embedded desingularization with smooth centres; the model space is part of the input, as for IdealSheafPair.

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                            noncomputable abbrev AnalyticManifold.EmbeddedPair.pullback {𝕜 : Type} [RCLike 𝕜] (T : EmbeddedPair 𝕜) {N : AnalyticManifold 𝕜 T.E} (g : AnalyticMap N T.M) (hg : IsLocalDiffeomorph (modelWithCornersSelf 𝕜 T.E) (modelWithCornersSelf 𝕜 T.E) ⊤ ⇑g) :

                            The pull-back (N, g^{-1}(Y)) of the embedded pair (M, Y) along a local analytic isomorphism g : N → M of manifolds modelled on E: the source of the morphism of embedded pairs over g [Wlo09, Theorem 3.5.1]. The pulled-back ideal sheaf is reduced (IdealSheaf.isReduced_pullback_of_isLocalDiffeomorph).

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                              The functoriality of an assignment on embedded pairs #

                              A compatible family assignment R on the embedded pairs (M, Y) commutes with local analytic isomorphisms: for a local analytic isomorphism g : N → M of manifolds modelled on one space and the embedded pair (N, g^{-1}(Y)), the family R(N, g^{-1}(Y)) is the pull-back of R(M, Y) along g (ExtensionCompatibleFamily.IsPullbackAlong): for compacts K' ⊆ N, K ⊆ M with g(U_{K'}) ⊆ U_K, the succession of R(N, g^{-1}(Y)) over U_{K'} is the pull-back along g of the succession of R(M, Y) over U_K, up to blow-ups with empty centre.

                              Relation to the source.

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                                A compatible family assignment R on the embedded pairs commutes with closed embeddings of ambient manifolds: for embedded pairs (M, Y) and (N, Y') and a closed embedding of analytic manifolds τ : N → M along which the ideal sheaf of Y is the push-forward of that of Y' (IdealSheaf.IsPushforwardAlong: τ(N) a closed submanifold containing Y, and Y' = τ^{-1}(Y)), such that no connected component of N lies in Y' (the ideal sheaf of Y' has nonzero stalks), the family R(M, Y) is the push-forward of R(N, Y') along τ (ExtensionCompatibleFamily.IsPushforwardAlong): for compacts K' ⊆ N, K ⊆ M with τ(U_{K'}) ⊆ U_K, the succession of R(M, Y) over U_K is the push-forward along τ of the succession of R(N, Y') over U_{K'}, up to blow-ups whose centres lie outside the part over τ(U_{K'}).

                                Relation to the source.

                                • Translation. EmbeddedPair.CommutesWithClosedEmbeddings R is the second half of [Wlo09, Theorem 2.0.2 (4)], "the morphism $\mathrm{res}_{Y,M}$ … commutes with … embeddings of ambient varieties", read as Kollár's commutation with closed embeddings [Kol07, 34.3] over every pair of compact sets, as IdealSheafPair.CommutesWithClosedEmbeddings reads the last sentence of [Wlo09, Theorem 2.0.3]: for a closed embedding $\tau \colon N \hookrightarrow M$ and a reduced $Y \subseteq N$, the embedded desingularization of $Y \subseteq M$ is the push-forward of that of $Y \subseteq N$, the stages of the succession over $N$ embedding over $\tau$ into those of the succession over $M$.
                                • Restatement. The clause is asserted when no connected component of $N$ lies in $Y$, Kollár's "$0 \neq I_Y$" (T'.Y.IsNonzeroEverywhere): on such a component the embedded desingularization of $Y \subseteq N$ is trivial, while that of $Y \subseteq M$ may blow up centres on it, where other components of $Y$ meet it.
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