The label coherence of the doubled datum #
Kollár's agreement of the centres on the overlaps, (37.2) in [Kol07, Proposition 37, proof], for
two runs. The coproduct member of label l of a datum D is traced on every piece (pieceTrace,
CoproductGluedFamily.lean), and the gluing of the pieces' local resolutions needs these traces to
be compatible along the transitions WITH THE IDENTITY LABELLING. The transitions come from the
DOUBLED datum sumPadData D D — the datum padded to the left and to the right, read on one
coproduct ambient — through the mixed-pair transition exists_mixedTransition_sumPadData
(CoproductMixedTransition.lean), whose member clause is stated at the labels σ of the doubled
run. A label l of D reaches the doubled run's stage set by TWO routes, lab₁ ∘ o₁.symm (the
padding identity of the left copy, then the label embedding at inl of CoproductSumData.lean)
and lab₂ ∘ o₂.symm (the right copy, inr), and the identity labelling of the traces needs the
two routes to AGREE — on the labels whose member is not the unit ideal (⊤ in the closed-subspace
order is the unit ideal, the EMPTY subspace, isUnit_iff; the off-range clauses of the label
embeddings say nothing about a label with an empty member, so the routes need not agree there, and
there the traces are all ⊤ and compatibility is trivial).
exists_resIn_toFun_eq: the coproduct local resolution is covered by the summand inclusionsresIn i(range_toFun_resIn,coe_sigmaCoordImage).exists_mem_support_comap_resIn_of_ne_top: a non-unit closed subspace of the coproduct local resolution has a point on some piece.sumLabelTrace: the⊤-extended piece trace along a label embedding into a common label set, with its two evaluation lemmas — the families of the conjugation lemma ofCoproductGluedFamilyCompat.lean.comap_sumInrResIn_sigmaMembers_ne_top_iff: the POINTWISE STEP — a stage of the doubled run has a non-empty trace on theinrcopy iff on theinlcopy: a point of one trace lies on a piece, its image inXlies in both piece domains (pieceDom_padAlongData), the mixed-pair transition at the same piece on both sides gives an isomorphism over a neighbourhood carrying the one trace to the other, and supports transfer along the inverse image (cosupport_comap).label_route_eq_of_ne_top: the two label routes agree on the non-trivial labels — the routes restricted to those labels are order embeddings of a finite linear order with equal ranges (OrderEmbedding.range_inj,Finite.to_wellFoundedLT; finiteness throughfinite_nonempty_totalTransformSeq).
No swap of the doubled ambient, no transport of the run, no non-emptiness of members is used anywhere. Not in the sources beyond Kollár's proof; bookkeeping.
A point of the cosupport of an ideal sheaf witnesses that it is not the unit ideal
(cosupport_top).
Four bookkeeping facts about the inverse image of ideal sheaves along a morphism of locally
ringed spaces (QuotientSpace.comap), stated once here for this module and the modules above it:
the unit ideal pulls back to the unit ideal, a non-unit inverse image comes from a non-unit ideal,
a point of the cosupport witnesses a non-unit ideal, and an isomorphism preserves non-unit ideals
(cosupport_comap: the cosupport of the inverse image is the preimage of the cosupport).
The inverse image of the unit ideal is the unit ideal (its cosupport is the preimage of the empty set).
An ideal sheaf whose inverse image is not the unit ideal is not the unit ideal.
Along an isomorphism the inverse image of a non-unit ideal sheaf is not the unit ideal — a
point of the cosupport has a preimage (cosupport_comap).
The coproduct local resolution is covered by the summand inclusions — every point lies in
the range of some resIn i (its image in the coproduct ambient lies in one summand of
ambImage W = ⋃ i, sigmaMk i '' W i, coe_sigmaCoordImage; range_toFun_resIn).
A non-unit closed subspace of the coproduct local resolution has a point on some piece —
the unit ideal is the closed subspace with empty support (isUnit_iff), and supports transfer
along resIn i (cosupport_comap).
The ⊤-extended piece trace along a label embedding — for a label σ of a common label
set, the trace on piece i of the member of D carried by o from the label k with
lab k = σ, and the unit ideal off the range of lab.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The extended trace at a label in the range is the trace of the member (lab is injective).
The extended trace at a label off the range is the unit ideal.
A stage of the doubled run has a non-empty trace on the inr copy iff on the inl copy
((37.2) in [Kol07, Proposition 37, proof], on the diagonal pair) — THE POINTWISE STEP, with no
labels: a point of one trace lies on a piece (exists_mem_support_comap_resIn_of_ne_top), its
image lies in both piece domains (pieceDom_padAlongData and hpre), the mixed-pair transition
at that piece on both sides carries the traces of every stage into each other over a
neighbourhood of the point, and supports transfer along the inverse image (cosupport_comap; from
the inr side through the inverse of the transition, comap_ne_top_of_isIso; the converse because
a non-unit inverse image comes from a non-unit ideal, ne_top_of_comap_ne_top).
The two label routes of the doubled datum agree on the non-trivial labels ((37.2) in
[Kol07, Proposition 37, proof], on the diagonal pair (D, D)) — for a label l of D whose
coproduct member is not the unit ideal, lab₁ (o₁.symm l) = lab₂ (o₂.symm l), where o₁, ψ₁
(resp. o₂, ψ₂) are the coproduct-level conjuncts of the padding identity read at the datum's
reading opens V (exists_padIdentity_of_padPreimageOpens_eq: the order isomorphism of stage
sets and the isomorphism of coproduct local resolutions carrying the members) and lab₁ (resp.
lab₂) is the label embedding of the left (resp. right) copy into the doubled run with its two
clauses (CoproductSumData.lean). The routes restricted to the non-trivial labels are order
embeddings of a finite linear order; by comap_sumInrResIn_sigmaMembers_ne_top_iff each has its
range inside the other's; equal ranges force equality (OrderEmbedding.range_inj). Off the
non-trivial labels nothing is asserted: the label embeddings' witnesses are not determined at an
empty member.