The lift of a local analytic isomorphism to the blowings-up #
The pull-back of a blow-up sequence along a smooth morphism h : Y → X has the stages
X_i ×_X Y and the centres Z_i ×_X Y; if h is surjective the pull-back determines the
sequence, while for a non-surjective h the pull-back may contain empty blow-ups, and the
information about the centres above X ∖ h(Y) is lost [Kol07, 30.1]. On analytic
manifolds the fibre product X_i ×_X Y along a local analytic isomorphism is replaced by the
blowing-up of the preimage centre h_i^{-1}(Z_i), which is identified with it by the uniqueness of
the blowing-up [BM88, Definition 4.1] (a local analytic isomorphism is flat, and blowing up
commutes with flat base change). The preimage h⁻¹(Y) of a closed submanifold of codimension c
under a local analytic isomorphism h : N → M is a closed submanifold of codimension c
(IsClosedSubmanifold.preimage_of_isLocalDiffeomorph, Hironaka/Manifold/Chart/Transport.lean).
This module provides the one-step lemmas, on manifolds that are not bundled:
blowUpLift: for blowings-upπ : M' → MofMalongYandπ' : N' → NofNalongh⁻¹(Y), the lifth' : N' → M'ofhover the blow-downs,π ∘ h' = h ∘ π'(blowDown_blowUpLift): the liftsliftPointGof the local inverses ofhto the blowings-up, glued (well defined by the uniqueness of lifts,IsBlowUp.eqOn_of_comp_eq_of_image_eq); it is a local analytic isomorphism (isLocalDiffeomorph_blowUpLift);- for any continuous
G : N' → M'overh(in particular the lift):Gagrees with the lift of every local inverseΦofhonπ'⁻¹(Φ.source)(eqOn_liftPartialDiffeomorph_of_comm), is surjective whenhis (surjective_of_comm), injective whenhis (injective_of_comm), and an open embedding whenhis (isOpenEmbedding_of_comm, for a local analytic isomorphismG).
The empty cases need no positive-codimension proviso: a point of N' over h (π' q) produces a
point of M' (exists_blowDown_eq_apply), and conversely a point of M' over h b produces a
point of N' over b (exists_blowDown_eq_of_blowDown_eq), through the blow-up charts (which
exist exactly where the codimension is positive) off and on the centre.
These lemmas are the steps of the pull-back of a whole sequence of centres in CenterList.lean
(BlowUpSequence.pullback).
The lift of a local analytic isomorphism to the blowings-up #
Over the image h (π' q) of a point of N' lies a point of M': off the centre by the
bijection off the exceptional divisor, on the centre through a blow-up chart (whose existence,
IsBlowUp.cover, forces the codimension to be positive) and the surjectivity of π.
Over a point b of N whose image h b is a blow-down lies a point of N' (the converse of
exists_blowDown_eq_apply, by the same case distinction).
The lift of h to the blowings-up, glued from the lifts liftPointG of the chosen local
inverses of h at the blow-downs of the points (Classical.choose on
(hh (π' q)).exists_partialDiffeomorph, the partial diffeomorphism agreeing with h near
π' q).
Equations
- Manifold.blowUpLiftAux hY hh hπ hπ' q = Manifold.liftPointG ⋯.choose ⋯ ⋯ hπ' hπ q
Instances For
The lifts of two local inverses of h agree at a point over both sources (uniqueness of
lifts, IsBlowUp.eqOn_of_comp_eq_of_image_eq on π'⁻¹(Φ.source ∩ Ψ.source)).
The glued lift agrees with the lift of any local inverse Φ of h over Φ.source.
The glued lift lies over h: π ∘ h' = h ∘ π'.
The glued lift is a local analytic isomorphism: at q₀ it agrees with the partial
diffeomorphism liftPartialDiffeomorph lifting the local inverse chosen at π' q₀.
A local analytic isomorphism h : N → M lifts to a local analytic isomorphism h' : N' → M'
of the blowings-up of N along h⁻¹(Y) and of M along Y, over the blow-downs (the lifts of
the local inverses, glued). If M' is empty so is N', and the lift is the empty map.
The lift h' : N' → M' of a local analytic isomorphism h : N → M to the blowings-up of
N along h⁻¹(Y) and of M along Y, over the blow-downs (π ∘ h' = h ∘ π',
blowDown_blowUpLift): the lifts of the local inverses of h, glued (chosen from
exists_blowUpLift). It plays the role of the map X_{i+1} ×_X Y → X_{i+1} of the pull-back
[Kol07, 30.1].
Equations
- Manifold.blowUpLift hY hh hπ hπ' = ⋯.choose
Instances For
The lift lies over h: π ∘ h' = h ∘ π', the commutative square of the pull-back.
The lift is a local analytic isomorphism.
The lift is analytic.
Properties transferred from h to any map over h (uniqueness of lifts) #
A continuous map G : N' → M' over h agrees with the lift of every local inverse Φ of h
on π'⁻¹(Φ.source) (uniqueness of lifts).
A continuous map over a surjective h is surjective (the surjective case of
[Kol07, 30.1]): a point p of M' lies over h b, and the lift of the local
inverse of h at b maps π'⁻¹(Φ.source) onto π⁻¹(Φ.target) ∋ p.
A continuous map over an injective h is injective: two points with the same image lie over
the same b, and the lift of the local inverse at b is injective on π'⁻¹(Φ.source).
A local analytic isomorphism G over an open embedding h is an open embedding (the
open-embedding case, the second of the two situations in which a blow-up sequence functor is
required to commute with smooth morphisms [Kol07, 34.1]).
The lift of a surjective local analytic isomorphism is surjective [Kol07, 30.1].
The lift of an injective local analytic isomorphism is injective.
The lift of an open embedding is an open embedding (the open-embedding case of [Kol07, 34.1]).
The exceptional divisor pulls back: h'⁻¹(π⁻¹(Y)) = π'⁻¹(h⁻¹(Y)) (Kollár's F_{i+1} ×_X Y).