The order clause along the pull-back by a local analytic isomorphism #
The compatible-family form of Step 2.1 (Step21Fam.lean) restricts sequences of centres along the
open inclusions M.restrict V → M.restrict W of a shrinking chain, local analytic isomorphisms
that are not surjective. The transport of the clauses of [Kol07, Definition 66] along a pull-back
proved in Functor/PullbackSequence.lean (isOfOrderGe_of_pullback) goes the other way and needs
surjectivity, because the reduced boundary red(π⁻¹E ∪ π⁻¹Z) of the successions
(IdealSheaf.reducedTransform; clause (iii) of [Hir64, Main Theorem II′(N)]) is defined by a
global case split on the existence of local generators, which descends only along surjections.
Forward, under the normal-crossings clause (3′) itself, no case split is needed: the boundary at
every stage is the reduced ideal sheaf of a family with simple normal crossings
(reducedTransform_eq_idealSheaf_totalTransform), such families pull back along local
isomorphisms (isSnc_comap), their reduced ideal sheaves are the pull-backs
(idealSheaf_comap_of_isSnc), and the total transform of a family pulls back along the lift
(totalTransform_comap_liftStep). This is the local nature of the functoriality package noted in
[Kol07, 104, Step 2.3] ("the functoriality package is local").
BlowUpSequence.isOfOrderGe_pullback— a sequence of order≥ mfor(𝓘, m, red E)pulls back along any local analytic isomorphismhto a sequence of order≥ mfor(h^* 𝓘, m, red h⁻¹E);AnalyticTriple.isOfOrderGe_pullbackis its form for triples;BlowUpSequence.isOfOrderGe_shrinkAppend— the shrink-and-append step of the chain (FamilyChain.lean) keeps the order clause for the restricted triple;AnalyticTriple.pullback_inclusion_restrictLE,pullback_eq_of_eq— restricting a restricted triple, and pull-backs along equal maps.
These are the order clauses carried by the chain of Step21Fam.lean and by Step 2.2 in the
compatible-family form (Step22Fam.lean).
The reduced ideal sheaf of h⁻¹(E) is the pull-back of the reduced ideal sheaf of E, for a
family E with simple normal crossings and a local analytic isomorphism h (no surjectivity is
needed): both sides fall under the first branch of the definition (the vanishing stalks of such a
family have local generators, IsSnc.hasLocalGenerators_vanishingStalk_support), and the
vanishing stalks correspond along the bijective germ maps. Not in the sources.
The order clause pulls back along any local analytic isomorphism (the local nature of
[Kol07, 34.1]): a sequence of order ≥ m for (𝓘, m, red E), E with simple normal crossings,
pulls back to a sequence of order ≥ m for (h^* 𝓘, m, red h⁻¹E). By recursion on the sequence
through isOfOrderGe_cons_iff: the normal-crossings clause and the order clause at the first
centre transport along h (comap_of_isLocalDiffeomorph,
ordAlongIdeal_comap_of_isLocalDiffeomorphAt); for the tail, the boundary after the first
blow-up is the reduced ideal sheaf of the total transform of E, a family with simple normal
crossings, on both sides (reducedTransform_eq_idealSheaf_totalTransform), the controlled
transform pulls back along the lift (birationalTransform_comap_liftStep), and the total transform
of h⁻¹E is the pull-back of the total transform of E (totalTransform_comap_liftStep).
The order clause pulls back, for triples: a sequence of order ≥ m starting with T pulls
back along any local analytic isomorphism to a sequence of order ≥ m starting with the
pulled-back triple.
Pulling back along equal maps gives equal triples.
Restricting the restriction of a triple to W further to V ≤ W is its restriction to V
(inclusion W ∘ restrictLE = inclusion V).
The inclusion of the lifted range after the corestriction is the lift itself.
The shrink-and-append step of the chain keeps the order clause: the sequence so far pulled back
to the smaller open is of order ≥ m for the restricted triple (isOfOrderGe_pullback), and the
appended value, of order ≥ m for the induced triple restricted to the reading open, pulls back
along the corestricted lift to a sequence of order ≥ m for the induced triple of the restricted
sequence (induced_pullback), so the concatenation is of order ≥ m (isOfOrderGe_concat).