Uniqueness of the blowing-up up to a unique diffeomorphism #
Conditions (1) and (2) of [BM88, Definition 4.1] define the blowing-up π : M' → M uniquely, up
to an isomorphism of M' commuting with π. For two blowings-up π₁ : M₁' → M, π₂ : M₂' → M
of M with centre Y:
- uniqueness of lifts: two continuous maps
G, G' : N → M₂'(N ⊆ M₁'open) withπ₂ ∘ G = π₂ ∘ G' = π₁agree: off the exceptional divisorπ₂is injective, and the complement of the divisor is dense (in a blow-up chart it is{u_i ≠ 0}); - the lift:
g pis the unique point overπ₁ poff the divisor whenπ₁ p ∉ Y, andΦ₂⁻¹(Φ₁ p)for blow-up chartsΦ₁,Φ₂of the same index over one adapted chart atπ₁ pwhenπ₁ p ∈ Y(their targets coincide: the full model chart domain); near every pointgis given by such a chart formula (by uniqueness of lifts), so it is analytic; the lift in the other direction is a two-sided inverse (uniqueness of lifts again), and any diffeomorphism commuting with the blow-downs equalsg.
The uniqueness statement is IsBlowUp.exists_unique_diffeomorph; the source states it without
proof. It is what allows the blowing-up to be transported along isomorphisms
(Hironaka.Manifold.BlowUp.Functor).
Blow-up charts of one index over one adapted chart #
Two blow-up charts of the same index over one adapted chart have the same target.
Φ₂⁻¹ ∘ Φ₁ lifts π₁ to π₂.
The chart change Φ₂⁻¹ ∘ Φ₁ between blow-up charts of the same index over the same adapted
chart, for two blowings-up, is analytic on Φ₁.source (both charts read the same coordinates).
Density of the complement of the divisor and uniqueness of lifts #
The complement of the exceptional divisor is dense: in a blow-up chart it is {u_i ≠ 0}.
Uniqueness of lifts: two continuous maps over π₁ into the second blowing-up agree on an open
set.
The lift #
An adapted chart at a point of the centre.
Equations
- Manifold.adChart hY ha = ⋯.choose
Instances For
Its block embedding.
Equations
- Manifold.adEmb hY ha = ⋯.choose
Instances For
The chosen adapted chart at a point of Y contains it and is adapted.
The index of a blow-up chart of π₁ at p over the adapted chart.
Equations
- Manifold.bIdx hY h₁ p hp = ⋯.choose
Instances For
A blow-up chart of π₁ at p.
Equations
- Manifold.bChart₁ hY h₁ p hp = ⋯.choose
Instances For
The chosen blow-up chart of π₁ at p is a blow-up chart containing p.
A blow-up chart of π₂ of the same index over the same adapted chart.
Equations
- Manifold.bChart₂ hY h₁ h₂ p hp = ⋯.choose
Instances For
The chosen blow-up chart of π₂ over the same adapted chart and index is a blow-up chart.
The lift of π₁ to π₂: over the centre Φ₂⁻¹ ∘ Φ₁ in blow-up charts of one index over one
adapted chart, off the centre the unique point of M₂' off the divisor over π₁ p.
Equations
- Manifold.liftPoint hY h₁ h₂ p = if hp : π₁ p ∈ Y then ↑(Manifold.bChart₂ hY h₁ h₂ p hp).symm (↑(Manifold.bChart₁ hY h₁ p hp) p) else Exists.choose ⋯
Instances For
Over the centre the lift is read through the chosen blow-up charts.
Off the centre the lift is the unique preimage under π₂ of π₁ p.
The lift commutes with the blow-downs: π₂ ∘ liftPoint = π₁.
Off the centre, liftPoint is the unique point off the divisor over 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 ∘ π₁ for a local inverse Ψ of π₂.
The lift is analytic.
The lift is a two-sided inverse of the lift in the other direction.
Uniqueness up to a unique diffeomorphism #
The diffeomorphism between two blowings-up of M with centre Y.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Two blowings-up of M with centre Y are isomorphic over M by a unique diffeomorphism
[BM88, Definition 4.1].