Functoriality of the blowing-up under local isomorphisms #
An analytic isomorphism g between open subsets U₁ ⊆ M₁, U₂ ⊆ M₂ carrying Y₁ ∩ U₁ onto
Y₂ ∩ U₂ lifts to a unique analytic isomorphism π₁⁻¹(U₁) → π₂⁻¹(U₂) over g between
blowings-up with centres Y₁, Y₂ (IsBlowUp.exists_lift_partialDiffeomorph). This is the
functoriality of the blowing-up under local isomorphisms, the case of an isomorphism onto an open
subset of the pull-back of a blow-up along a smooth morphism [Kol07, Definition 30, 30.1]; it
follows from the uniqueness clause of [BM88, Definition 4.1]. The lift is built as in
Hironaka.Manifold.BlowUp.Unique: over the centre by blow-up charts of one index over an
adapted chart φ₁ of Y₁ at π₁ p and its transport φ₁ ∘ g⁻¹ (an adapted chart of Y₂), off
the centre as the unique point off the divisor over g(π₁ p); uniqueness of lifts (density of
the complement of the divisor, injectivity of π₂ off Y₂) gives the local chart formulas, the
inverse and the uniqueness clause. The first ingredient is that a chart of the maximal atlas
composed with the inverse of a partial diffeomorphism is a chart of the maximal atlas of the
target (transportChart, Hironaka/Manifold/Chart/Transport.lean). The centres are required to
have positive codimension: for c = 0 no total map M₁' → M₂' need exist.
This functoriality is what makes the blowing-up, and the sequences of blowings-up built from it,
compatible with local isomorphisms of the ambient manifold
(Hironaka.Manifold.FiniteSuccession.Lift,
Hironaka.Manifold.FiniteSuccession.Restrict.Transport).
The lift of a partial diffeomorphism carrying the centres to each other #
Φ₂⁻¹ ∘ Φ₁ lifts π₁ to π₂ over g, for blow-up charts of one index over an adapted chart
and its transport.
The chart change between a blow-up chart of π₁ over φ and a blow-up chart of π₂ over the
transported chart is analytic on the source (the two charts read the same coordinates through g).
Uniqueness of lifts over g: two continuous maps over g ∘ π₁ into the second blowing-up
agree on an open subset of π₁⁻¹(g.source).
The chart data at a point over the centre #
The adapted chart at a point of the centre, restricted to the source of g.
Equations
- Manifold.adChartG g hY₁ ha = (Manifold.adChart hY₁ ha).restrOpen g.source ⋯
Instances For
The chosen adapted chart at a, cut down to g.source, is adapted to Y₁.
The cut-down adapted chart has source inside g.source.
A point of Y₁ ∩ g.source lies in the source of its cut-down adapted chart.
The index of a blow-up chart of π₁ at p.
Equations
- Manifold.bIdxG g hY₁ h₁ hp hY = ⋯.choose
Instances For
A blow-up chart of π₁ at p.
Equations
- Manifold.bChart₁G g hY₁ h₁ hp hY = ⋯.choose
Instances For
The chosen blow-up chart of π₁ at p over the cut-down adapted chart is a blow-up chart
containing p.
A blow-up chart of π₂ of the same index over the transported adapted chart.
Equations
- Manifold.bChart₂G g hg hY₁ h₁ h₂ hp hY = ⋯.choose
Instances For
The chosen blow-up chart of π₂ over the transported chart (same block indices and index) is a
blow-up chart.
The lift of π₁ to π₂ over g: over the centre Φ₂⁻¹ ∘ Φ₁ in blow-up charts of one index
over an adapted chart and its transport, off the centre the unique point of M₂' off the divisor
over g (π₁ p); an arbitrary point outside π₁⁻¹(g.source).
Equations
- One or more equations did not get rendered due to their size.
Instances For
Over the centre the lift of g is read through the chosen blow-up charts.
The lift commutes with the blow-downs over g: π₂ ∘ liftPointG = g ∘ π₁ on π₁⁻¹(g.source).
Off the centre, the lift is the unique point off the divisor over g (π₁ p).
Near a point over the centre, the lift is the chart formula Φ₂⁻¹ ∘ Φ₁.
Near a point off the centre, the lift is Ψ⁻¹ ∘ g ∘ π₁ for a local inverse Ψ of π₂.
The lift is analytic on π₁⁻¹(g.source).
The lift of g maps π₁⁻¹(g.source) into π₂⁻¹(g.target).
The lift as a partial diffeomorphism #
The lift in the other direction inverts the lift on π₁⁻¹(g.source) (uniqueness of lifts of
π₁ to itself).
The lift of g as a partial diffeomorphism M₁' → M₂' with source π₁⁻¹(g.source) and
target π₂⁻¹(g.target).
Equations
- One or more equations did not get rendered due to their size.
Instances For
Functoriality under local isomorphisms #
Functoriality under local isomorphisms: an analytic isomorphism g between open subsets
with g(Y₁ ∩ U₁) = Y₂ ∩ U₂ lifts to an analytic isomorphism π₁⁻¹(U₁) → π₂⁻¹(U₂) over g,
unique as a map on π₁⁻¹(U₁); the centres have positive codimension. This is the pull-back of a
blow-up along an isomorphism onto an open subset [Kol07, Definition 30, 30.1], and the uniqueness
is that of [BM88, Definition 4.1].