Isomorphisms over a base, glued along an open cover of the base #
The resolutions of two pieces of a cover are identified over their overlap: the resolution is
independent of the chosen embedding up to a canonical isomorphism [Kol07, Theorem 36, proof], and it
commutes with open embeddings [Kol07, 44] and with local analytic isomorphisms [Wlo09, §4]. When an
isomorphism over the base between two resolutions of one open subset is unique, the identifications
given on the members of an open cover of the overlap agree where the members meet, and glue to one
over the whole overlap. That is the statement here, for K-locally-ringed spaces over a base with
the uniqueness as hypothesis. Two K-locally-ringed spaces A, B over Z (πA, πB), an open
subset O ⊆ Z covered by open subsets N i ≤ O, and isomorphisms s i : A|πA⁻¹(N i) ≅ B|πB⁻¹(N i)
over Z, unique among such on every open subset O' ≤ O: they glue to an isomorphism
A|πA⁻¹O ≅ B|πB⁻¹O over Z.
KLocallyRingedSpace.restrictOver: the restriction of a morphism overZbetween the parts overPto the parts overQ ≤ P, with its compatibility lemmas; an isomorphism overZrestricts to an isomorphism (isIso_restrictOver), and uniqueness of isomorphisms overZfromAtoBgives uniqueness fromBtoA(uniq_symm).KLocallyRingedSpace.glueIsoPieces: the morphismA|πA⁻¹O ⟶ B|πB⁻¹Oassembled from thes ibyglueOfCoveron the cover ofA|πA⁻¹Oby the parts over theN i; the pieces agree on the overlaps by the uniqueness atN i ⊓ N j(gluePiece_compatible); it lies overZ(glueIsoPieces_over) and restricts to the pieces (ofRestrict_comp_glueIsoPieces).KLocallyRingedSpace.glueIsoPieces_comp_glueIsoPieces: the assemblies of two piecewise inverse families are inverse (hom_ext_of_cover).KLocallyRingedSpace.exists_isIso_over_of_cover: the statement.
The restriction restrictOver is the transition of a gluing datum restricted to the parts over a
smaller base open subset (Hironaka.Resolution.Analytic.Kol07Thm45.Glue.OverRigidity,
Hironaka.Resolution.Analytic.Kol07Thm45.PieceTransitionGlue, PieceGlueIndep,
ResolutionFunctorial, RigidOverLocalResolution, CoproductLevelPair);
exists_isIso_over_of_cover gives the transition isomorphisms between the local resolutions of two
pieces over their overlap (Hironaka.Resolution.Analytic.Kol07Thm45.PieceTransitionGlue,
PieceGlueIndep, ResolutionFunctorial,
Hironaka.Resolution.Analytic.Kol07Thm45.RestrictSetIncl).
Restricting a morphism over Z to a smaller open of the base #
A morphism over Z preserves the point of the base.
The restriction of a morphism over Z between the parts over P to the parts over Q ≤ P:
the lift of A|πA⁻¹Q ⟶ A|πA⁻¹P ⟶ B|πB⁻¹P ⟶ B through B|πB⁻¹Q ⟶ B.
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The restriction of s to the parts over Q lies over s: followed by the inclusion of
B|πB⁻¹Q into B it is the inclusion of A|πA⁻¹Q into A|πA⁻¹P followed by s and the inclusion
into B (liftRestrict's factorization).
The restriction of s to the parts over Q lies over s: followed by the inclusion of
B|πB⁻¹Q into B it is the inclusion of A|πA⁻¹Q into A|πA⁻¹P followed by s and the inclusion
into B (liftRestrict's factorization).
The restriction of s to the parts over Q, followed by the inclusion of open subspaces
B|πB⁻¹Q ⟶ B|πB⁻¹P, is the inclusion A|πA⁻¹Q ⟶ A|πA⁻¹P followed by s (both sides agree after
the open immersion into B).
The restriction of s to the parts over Q, followed by the inclusion of open subspaces
B|πB⁻¹Q ⟶ B|πB⁻¹P, is the inclusion A|πA⁻¹Q ⟶ A|πA⁻¹P followed by s (both sides agree after
the open immersion into B).
The restriction of a morphism over Z is over Z.
The inverse of an isomorphism over Z is over Z.
The restrictions of two piecewise inverse morphisms over Z are inverse.
An isomorphism over Z restricts to an isomorphism over Z.
Uniqueness of the isomorphisms over Z from the parts of A to the parts of B over every
open O' ≤ O gives the uniqueness of those from B to A: the inverses are isomorphisms over Z
from A to B.
The gluing of the local isomorphisms #
The cover of A|πA⁻¹O by the parts over the N i.
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A point of A|πA⁻¹O lies in the i-th member of the cover iff its base point lies in N i
(definitional).
The parts over the N i cover A|πA⁻¹O, since the N i cover O.
The inclusion of a member of the cover into the part of A over N i.
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The inclusion of a member of the cover into A|πA⁻¹(N i), followed by the open immersion into
A, is the composite of the two open immersions (A|πA⁻¹O)|_{cover} ⟶ A|πA⁻¹O ⟶ A
(liftRestrict's factorization).
The inclusion of a member of the cover into A|πA⁻¹(N i), followed by the open immersion into
A, is the composite of the two open immersions (A|πA⁻¹O)|_{cover} ⟶ A|πA⁻¹O ⟶ A
(liftRestrict's factorization).
The piece of the gluing over N i: s i on the part over N i, followed by the inclusion
into B|πB⁻¹O.
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The i-th piece of the gluing, followed by the open immersion B|πB⁻¹O ⟶ B, is
pieceIncl i ≫ s i followed by the open immersion B|πB⁻¹(N i) ⟶ B (liftRestrict's
factorization).
The i-th piece of the gluing, followed by the open immersion B|πB⁻¹O ⟶ B, is
pieceIncl i ≫ s i followed by the open immersion B|πB⁻¹(N i) ⟶ B (liftRestrict's
factorization).
The pieces agree on the overlaps: both restrictions to the part over N i ⊓ N j are
isomorphisms over Z, hence equal by the uniqueness hypothesis.
The morphism A|πA⁻¹O ⟶ B|πB⁻¹O glued from the local isomorphisms s i along the cover of
A|πA⁻¹O by the parts over the N i.
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The glued morphism restricts to the i-th piece on the i-th member of the cover
(ofRestrict_comp_glueOfCover).
The glued morphism restricts to the i-th piece on the i-th member of the cover
(ofRestrict_comp_glueOfCover).
The glued morphism lies over Z.
The assemblies of two piecewise inverse families of isomorphisms over Z are inverse.
Isomorphisms over Z glue along an open cover of the base: isomorphisms over Z between
the parts of A and B over the members of an open cover of an open subset O ⊆ Z, unique among
such on every open subset of O, glue to an isomorphism over Z between the parts over O
(glueOfCover on the cover pulled back to A, hom_ext_of_cover).