Lemma 102 on analytic manifolds: the construction of the functor BD #
Kollár's Lemma 102 ([Kol07, Lemma 102]) is the first ingredient of order reduction for ideals: for
a triple (X, I, E) with max-ord I ≤ m and a member E^j of the boundary, assuming order
reduction for marked ideals in dimension n - 1, it produces a smooth blow-up sequence functor
BD_{n,m,j} of order m after which the cosupport cosupp(I_r, m) is disjoint from the
birational transform of E^j. Its proof first replaces I by the D-balanced ideal W_{m!}(I)
([Kol07, Corollary 101]; here W_s(𝓘) with s = tuningParam m, Tuned.lean) and then, with S := E^j, blows up the union Z_{-1} of the components
of E^j contained in cosupp(I, m), restricts the weak transform I_0 and the boundary E - E^j
to S, applies the marked functor BMO_{n-1,m} to the restricted triple and pushes the result
forward ([Kol07, 30.3]): BD_{n,m,j}(X, I, E) := τ_* BMO_{n-1,m}(S, I_0|_S, m, E_S) ∘ π_{-1}.
This module carries the construction out on analytic manifolds, in two layers as in the proof: a
core on D-balanced triples, and the functor itself on the tuned triple.
HypersurfaceFamily.emptyMember F j— Kollár'sE - E^j, with the index set kept and thej-th member replaced by the empty hypersurface;IsSnc.emptyMember, andIsSnc.hasSncWithProper_emptyMember: the other members have simple normal crossings withE^jproperly (at a point ofE^j, the chart of the simple normal crossings hasE^jas a coordinate hyperplane and the other members through the point on other coordinates).HypersurfaceFamily.HasSncWithProper.comap— proper simple normal crossings pull back along a local analytic isomorphism (the charts are transported along the local inverses).isLocalDiffeomorph_blowUpπ_of_codimOne— blowing up a hypersurface is a local analytic isomorphism ([Kol07, Warning 20]: a trivial blow-up is an isomorphism).BDan.BDClass s— the class of the core: the triples ofBOClass swhose ideal sheaf is D-balanced at the marks.BDan.transformS,BDan.weakTransformI,BDan.boundaryMinus,BDan.restrictedTriple— the transformS_0 = π_{-1}^{-1}(E^j)ofE^j, the weak transformI_0of𝓘, the pulled-backE - E^j, and the triple(S_0, I_0|_{S_0}, (E - E^j)|_{S_0})on the hypersurfaceS_0regarded as a manifold modelled on𝕜^{n-1}; its ideal sheaf is nonzero everywhere becauseI_0is D-balanced, and its boundary has simple normal crossings as the trace of a family having proper simple normal crossings withS_0. It lies in the marked classBMOClass s. They are the instances atZ_{-1}ofBDan.transformSOf,BDan.weakTransformIOf,BDan.boundaryMinusOf,BDan.restrictedTripleOf, over an arbitrary closed hypersurfaceZ(andS').BDan.coreOfListOf hZ hS' L— the core over a sequence: the blow-up of a closed hypersurfaceZ, followed by the push-forward of a sequenceLon a closed hypersurfaceS'of the blow-up, with empty blow-ups deleted ([Kol07, 32]);BDan.core s T j inp hT— the core:coreOfListOfatZ_{-1}andS_0over the value of the input functorinp : BMOanData 𝕜 (n - 1) son the restricted triple (the first blow-up is empty when no component ofE^jlies incosupp(𝓘, s)).BDan m inp T hT j— the functorBD_{n,m,j}on the classBOClass m: the core at the marks = tuningParam mon the tuned triple(M, W_s(𝓘), E)(Tuned.lean), the input beingBMO_{n-1,s}.
The clauses of Lemma 102 for BDan — order m with respect to E, the disjointness (1) and the
functoriality (2) — are proved in BDCore.lean, BDCosupp.lean, BDBridge.lean, BDOf.lean,
BDErase.lean and BDIndiff.lean, and carried over to the compatible-family form of
BDFam.lean, whose data bdanFamDataOfInput (BOanFamOfInput.lean) is the input of Steps 2.1 and
2.2 of the proof of Theorem 103.
The push-forward inside the core is the push-forward of a list of centres; its identification
with the push-forward of the corresponding succession of blow-ups
(BlowUpSequence.toSuccession_pushforward) holds for lists without empty centres and is what makes
[Kol07, Corollary 85] available for the clauses.
E − E^j: emptying a member #
Kollár's E - E^j (the proof of [Kol07, Lemma 102], "E_S := (E - E^j)|_S"): the family with
the same index set, the j-th member replaced by the empty hypersurface and the others unchanged.
Keeping the index set lets the member be named by its index throughout.
Equations
Instances For
A chart of the simple normal crossings of F at a is one of E - E^j at a: the members
through a other than E^j keep their coordinates.
E - E^j has simple normal crossings when E does.
The members of E other than E^j have simple normal crossings with E^j properly: at a point
of E^j, a chart of the simple normal crossings of E has E^j as the coordinate hyperplane of
the j-th index and is adapted to E^j, while the other members through the point use other
coordinates (the indices are injective). This is the hypothesis "E + H has simple normal
crossings" of [Kol07, Corollary 85] for H := E^j, needed for the restriction of E - E^j to
S = E^j in the proof of [Kol07, Lemma 102].
Proper simple normal crossings pull back along local analytic isomorphisms #
Proper simple normal crossings pull back along a local analytic isomorphism h : N → M: the
adapted chart and the chart of the simple normal crossings at h a are transported along a local
inverse of h, with the same coordinate indices.
Blowing up a closed hypersurface is a local analytic isomorphism ([Kol07, Warning 20]: the
blow-up of a Cartier divisor is an isomorphism): the blow-up map is a diffeomorphism
(IsBlowUp.exists_diffeomorph_of_codim_one).
Lemma 102's core #
The class of the core of Lemma 102 (the proof of [Kol07, Lemma 102], "from now on we assume
that I is D-balanced"): the triples of BOClass s whose ideal sheaf is D-balanced at the mark
s; the tuned triples of Tuned.lean belong to it.
Equations
Instances For
The first blow-up π_{-1} : X_0 → X of the proof of [Kol07, Lemma 102], with centre Z_{-1}.
Equations
- Hironaka.Manifold.BDan.piMinusOne T s j = Manifold.blowUpπ ψ₀ ⋯
Instances For
π_{-1} is a local analytic isomorphism ([Kol07, Warning 20]; its centre is a hypersurface).
The data of the core over an arbitrary closed hypersurface #
The transform π^{-1}(E^j) of the member E^j under the blowing-up of a closed hypersurface
Z (transformS at Z = Z_{-1}).
Equations
- Hironaka.Manifold.BDan.transformSOf T j hZ = ⇑(Manifold.blowUpπ ψ₀ hZ) ⁻¹' T.F.hyp j
Instances For
The weak transform of 𝓘 under the blowing-up of a closed hypersurface Z (weakTransformI
at Z = Z_{-1}).
Equations
Instances For
E - E^j pulled back along the blowing-up of a closed hypersurface Z (boundaryMinus at
Z = Z_{-1}).
Equations
- Hironaka.Manifold.BDan.boundaryMinusOf T j hZ = Manifold.HypersurfaceFamily.comap (⇑(Manifold.blowUpπ ψ₀ hZ)) (T.F.emptyMember j)
Instances For
The transform S_0 = π_{-1}^{-1}(E^j) of the member E^j under the isomorphism π_{-1}, the
hypersurface S := E^j of the proof of [Kol07, Lemma 102] read on X_0.
Equations
Instances For
S_0 is a closed hypersurface of the blown-up manifold.
The weak transform I_0 of 𝓘 under π_{-1} (the proof of [Kol07, Lemma 102], "we get a new
ideal sheaf I_0").
Equations
Instances For
The family E - E^j pulled back along the isomorphism π_{-1} (the proof of
[Kol07, Lemma 102], "E_S := (E - E^j)|_S", before the restriction to S).
Equations
Instances For
The pulled-back E - E^j has simple normal crossings.
The pulled-back E - E^j has simple normal crossings with S_0 properly (the hypothesis of
[Kol07, Corollary 85] on the boundary, for H := S_0).
The restricted triple (S, I_0|_S, E_S) of the proof of [Kol07, Lemma 102] over an arbitrary
closed hypersurface Z and an arbitrary closed hypersurface S' of its blow-up, with the
identifications Z = Z_{-1} and S' = S_0 as hypotheses used only in the proof fields (the pulled
back centre and transform are only propositionally Z_{-1} and S_0): the restriction of the weak
transform of 𝓘, nonzero everywhere because 𝓘 is D-balanced with ord 𝓘 ≤ s
(BD.isNonzeroEverywhere_pullback_weakTransformOf), and the trace of the pulled-back E - E^j,
with simple normal crossings as the trace of a family having proper simple normal crossings with
S_0.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The restricted triple (S, I_0|_S, E_S) of the proof of [Kol07, Lemma 102], on the hypersurface
S_0 regarded as a manifold modelled on 𝕜^{n-1} with the standard chart: restrictedTripleOf at
Z_{-1} and S_0.
Equations
- Hironaka.Manifold.BDan.restrictedTriple T s j hT = Hironaka.Manifold.BDan.restrictedTripleOf T s j ⋯ ⋯ hT ⋯ ⋯
Instances For
The restricted triple lies in the marked class BMOClass s: only finitely many of its members
are nonempty, since a nonempty member of the trace comes from a nonempty member of E.
The core over a sequence, over an arbitrary closed hypersurface Z of M and a closed
hypersurface S' of its blowing-up: the blowing-up of Z, then the push-forward of a sequence of
centres L on S' regarded as a manifold ([Kol07, Definition 30 (3)]), with empty blow-ups
deleted ([Kol07, 32]).
Equations
Instances For
The core of Lemma 102 (the proof of [Kol07, Lemma 102]: the value BMO_{n-1,m}(S, I_0|_S, m, (E - E^j)|_S) is pushed forward ([Kol07, 30.3]) and composed "on the right with our first blow-up
π_{-1}"): the core over the value of the input functor on the restricted triple, at Z_{-1} and
S_0 (the first blow-up is empty when no component of E^j lies in cosupp(𝓘, s)).
Equations
- Hironaka.Manifold.BDan.core T s j inp hT = Hironaka.Manifold.BDan.coreOfListOf ⋯ ⋯ (inp.functor.seq (Hironaka.Manifold.BDan.restrictedTriple T s j hT) ⋯)
Instances For
The value of the core has no empty centres ([Kol07, 32]).
The functor BD_{n,m,j} of [Kol07, Lemma 102] on analytic manifolds: on a triple of the
class BOClass m, the core at the mark s = tuningParam m applied to the tuned triple
(M, W_s(𝓘), E) (the proof's first step, the tuning to a D-balanced ideal with the same order
reduction,
[Kol07, Corollary 101], at the mark s in place of Kollár's m!), with the input functor
BMO_{n-1,s},
a BMOanData 𝕜 (n - 1) (tuningParam m). The member is named by its index j : T.F.ι, which
every pull-back keeps.
Equations
- Hironaka.Manifold.BDan m inp T hT j = Hironaka.Manifold.BDan.core (T.tuned m ⋯) (IsLocalRing.tuningParam m) j inp ⋯
Instances For
The value of BD_{n,m,j} has no empty centres ([Kol07, 32]).