The local resolution over a smaller open, and the relation "isomorphic over N" #
Kollár's proof of Theorem 36 compares the local resolutions of a piece for two embeddings NEAR a
point [Kol07, Theorem 36, proof]: localResolution_independent_local
(LocalResolutionShear.lean) asks for an open N of the piece and an isomorphism of the two local
resolutions restricted over N, compatible with the maps to the piece — the relation
LocIso N (A, pA) (B, pB) :≡ ∃ ψ : A|pA⁻¹N ≅ B|pB⁻¹N, pB|N ∘ ψ = pA|N (not given a name: the
theorems state it in full). This module provides:
- the relation is an equivalence —
AnalyticSpace.exists_restrictSet_isIso_trans,exists_restrictSet_isIso_symm— andexists_restrictSet_isIso_of_comp_eqfeeds it every global isomorphism over the piece; its open-immersion formexists_restrictSet_isIso_of_comp_eq_of_isOpenImmersion(an open immersionA → Bover the piece whose range coverspB⁻¹ Nrestricts to an isomorphism overN; theisoOfRangeEqmechanism with the isomorphism hypothesis weakened to the range condition, for OPENN— the restriction of a space to a non-open set is by convention the whole space,openOf); - the morphism
homOfPullbackEqof closed subspaces induced by an identityJ' = f^* Jalong an INJECTIVE local analytic isomorphismfis an open immersion with range the points overrange f(isOpenImmersion_homOfPullbackEq_of_injective,range_toFun_homOfPullbackEq) —isIso_homOfPullbackEq_of_diffeomorph's mechanism minus surjectivity; - the preimage of a relatively compact open under the zero extension is relatively compact
(
isCompact_closure_preimage_padExt); - restriction to a smaller open: for relatively compact opens
W' ≤ Wof the ambient, the compatibility fieldcompatof the family (Functor/Family.lean; the restriction of the factorization to a smaller open determines the factorization, [Wlo09, Theorem 2.0.2(5)]) gives the sequence overW'as the pull-back of the sequence overWalong the open inclusion with empty centres erased (localResolutionSeq_of_le); the last-stage liftliftOfLe(the lift of [Kol07, Definition 30.1], throughstageOfEq,eraseEmptyLast,pullbackLiftLast) is an injective local isomorphism over the inclusion with range the part overW'; the final strict transforms correspond (strictTransformSubspaceSeq_last_liftOfLe); so the induced morphism of closed subspaces is an open immersionlocalResolutionHomOfLe : Ỹ(W') → Ỹ(W)over the piece (localResolutionToPiece_comp_localResolutionHomOfLe) whose range covers everything over an openN ⊆ embPreimage W', andexists_restrictSet_isIso_localResolution_of_leis the open-immersion form of the relation at it.
Not in the sources beyond Kollár's comparison; bookkeeping (the lift of [Kol07, Definition 30.1] at an open inclusion; the functoriality of quotients).
The relation "isomorphic over N" is an equivalence #
The relation "(A, pA) and (B, pB) over Z are isomorphic over N compatibly with the
maps" is transitive: compose the two isomorphisms of the restrictions.
The relation is symmetric: the inverse isomorphism.
The open-immersion form of the restriction lemma #
An OPEN IMMERSION χ : A → B over Z (χ ≫ pB = pA) whose range contains pB⁻¹ N, for an
OPEN N, restricts to an isomorphism A|pA⁻¹N ≅ B|pB⁻¹N over Z|N — isoOfRangeEq of the two
open immersions A|pA⁻¹N → B and B|pB⁻¹N → B with equal ranges, the compatibility by
lift_uniq/lift_fac; the isomorphism hypothesis of exists_restrictSet_isIso_of_comp_eq
weakened to the range condition.
The relation "isomorphic over N" from an open immersion over the piece whose range covers
pB⁻¹ N, N open — the analytic-space form of
KLocallyRingedSpace.exists_restrictSet_isIso_of_comp_eq_of_isOpenImmersion.
The preimage of a relatively compact open under the zero extension #
The zero extension s : G → padOpens σ G is a closed embedding: a homeomorphism onto the
closed slice (padExtDiffeomorph, isClosed_padSlice). Internal.
The preimage under the zero extension of a relatively compact open is relatively compact:
closure (s⁻¹ U) ⊆ s⁻¹ (closure U), the preimage of a compact set under a closed embedding
(Topology.IsClosedEmbedding.isCompact_preimage).
The induced morphism of closed subspaces along an injective local isomorphism #
The morphism of closed subspaces induced by J' = f^* J along an INJECTIVE local analytic
isomorphism f is an open immersion: the base map is the restriction of the open embedding f to
the cosupports (cosupport_pullback_of_bijective with germMap_bijective_of_isLocalDiffeomorphAt,
Set.restrictPreimage_isOpenEmbedding), the fibre maps are bijective
(isIso_map_stalkMap_of_bijective), Mathlib's LocallyRingedSpace.IsOpenImmersion.of_stalk_iso —
isIso_homOfPullbackEq_of_diffeomorph's mechanism minus surjectivity.
The range of the induced morphism along a local analytic isomorphism: the points of Sp(A)/J
over the range of f (the cosupport of f^* J is the preimage of the cosupport of J,
cosupport_pullback_of_bijective).
The local resolution over a smaller open #
strictTransformSubspaceSeq_last_pullback_eraseEmpty' read through a sequence EQUAL to the
erased pull-back and an ideal EQUAL to the pulled-back ideal: the final strict transform of J'
along L' is the pull-back of the final strict transform of J along L under the lift
pullbackLiftLast ∘ eraseEmptyLast⁻¹ ∘ stageOfEq e (the lift of [Kol07, Definition 30.1]; subst
on both equalities, stageOfEq rfl the identity). Internal.
The compatibility field compat of the family (Functor/Family.lean) at the piece's triple
([Wlo09, Theorem 2.0.2(5)]): the sequence over W' is the pull-back of the sequence over W
along the open inclusion, empty centres erased.
The last-stage lift of the open inclusion W' ↪ W (the lift of [Kol07, Definition 30.1]
at an open inclusion): the transport stageOfEq along localResolutionSeq_of_le, then
eraseEmptyLast⁻¹, then pullbackLiftLast — an analytic map from the last stage of the sequence
over W' to the last stage of the sequence over W.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The lift is a local analytic isomorphism (isLocalDiffeomorph_pullbackLiftLast, two
diffeomorphisms).
The lift is injective (injective_pullbackLiftLast, the inclusion injective).
The lift lies over the open inclusion (stageMap_last_pullbackLiftLast,
stageMap_last_eraseEmptyLast_symm, stageMap_last_stageOfEq).
The range of the lift is the part of the last stage over W' (range_pullbackLiftLast).
The final strict transforms correspond under the lift:
strictTransformSubspaceSeq_last_pullback_eraseEmpty' with
strictTransformSubspaceSeq_last_stageOfEq and 𝓘|W' = (𝓘|W).comap (W' ↪ W) (pullback_comp).
The local resolution over W' maps into the local resolution over W (Kol07, Theorem
36, proof): the morphism of closed subspaces induced along the lift by
strictTransformSubspaceSeq_last_liftOfLe.
Equations
- E.localResolutionHomOfLe bed W hW W' hW' hle = Manifold.IdealSheaf.homOfPullbackEq ⇑(E.liftOfLe bed W hW W' hW' hle) ⋯ ⋯
Instances For
It is an open immersion (isOpenImmersion_homOfPullbackEq_of_injective at the injective local
isomorphism liftOfLe).
It lies over the piece: Π_W ∘ χ = Π_{W'} — Hom.ext_of_comp_quotientι on the square of
the composites through localResolutionMap_comp_ι, stageMap_last_liftOfLe,
homOfPullbackEq_comp_toAnalyticSpaceι and inclusion W ∘ restrictLE = inclusion W'.
Its range covers the part over N for N ⊆ embPreimage W': a point of Ỹ(W) over N
lies over W' (range_toFun_homOfPullbackEq, range_liftOfLe, the ambient point of Π_W q is
the composite of q).
Restriction to a smaller open (the value over W read over W' ⊆ W, Kol07, Theorem 36,
proof; the compatibility compat of the family, [Wlo09, Theorem 2.0.2(5)]): for relatively
compact opens W' ≤ W of the ambient and an open N of the piece lying over W', the local
resolutions over W and over W' are isomorphic over N compatibly with the maps to the piece —
exists_restrictSet_isIso_of_comp_eq_of_isOpenImmersion at the open immersion
localResolutionHomOfLe over the piece whose range covers the part over N, then
exists_restrictSet_isIso_symm for the orientation.