The Jacobian ideal and the monoidal transformations along a square across the models #
The chart-level notions of the vocabulary — adapted charts and closed submanifolds, the ideal
sheaf of a submanifold, blow-up charts, blowings-up and monoidal transformations
([BM88, Definition 4.1]), the Jacobian ideal ([BM97, Theorem 1.10, the sentence after it]) —
transport along a square f ∘ g' = g ∘ f' of
analytic isomorphisms g : N ≃ M, g' : N' ≃ M' across the models (IsModelSquare). The device is
one chart: chartOfSquare g ψ φ := ψ ∘ φ ∘ g, a chart of N read from a chart φ of M through
g and a linear isomorphism ψ : E ≃L[𝕜] E' of the models. It is in the maximal atlas of N
(mem_maximalAtlas_of_contMDiffOn), its source is g⁻¹(φ.source), and reading a chart of N
through g⁻¹, ψ⁻¹ and back gives the chart (chartOfSquare_chartOfSquare_symm).
- The predicates carry a chart isomorphism
ψ₀ : E ≃L[𝕜] (Fin n → 𝕜); onNit becomesψ.symm.trans ψ₀. An adapted chart ofMreads as an adapted chart ofNand back (IsAdaptedChart.of_square,of_square_symm), a closed submanifoldYpulls back tog⁻¹(Y), the ideal sheaf ofYpulls back to the ideal sheaf ofg⁻¹(Y)— the coordinate germs correspond under the stalk isomorphism ofg(stalkRingEquiv_coord), whatever the witnesses of the two submanifolds (IsClosedSubmanifold.idealSheaf_pullbackDiffeomorph) — and a blow-up chart offoverψ⁻¹ ∘ φ' ∘ g⁻¹reads as a blow-up chart off'overφ'(IsBlowUpChart.of_square), so a blowing-up transports (IsBlowUp.of_square) and with it a monoidal transformation (AnalyticMap.IsMonoidalTransformation.of_square). - The Jacobian: in the charts read from those of
f, the chart representative off'is the conjugateψ ∘ (φ ∘ f ∘ φ'⁻¹) ∘ ψ⁻¹of the representative off, so the Jacobian determinants are equal (LinearMap.det_conj,det_clm_conj) — no unit germs enter — and the Jacobian stalk transports along the stalk isomorphism ofg'(jacobianStalk_of_square), whence the Jacobian ideal (AnalyticMap.jacobianIdeal_of_square). This needs no model isomorphism: at a pointbofN'the inverse differential ofg'(Diffeomorph.mfderivToContinuousLinearEquiv) serves asψ. - The monoidal transformation takes the model isomorphism
ψ: the chart isomorphism ofNisψ.symm.trans ψ₀, and without someE ≃L[𝕜] E'the statement fails whenNandN'are empty andE'is not linearly isomorphic toFin n → 𝕜.
These are the steps by which the successions of the resolution are carried between the models
(Hironaka/Resolution/Analytic/ModelTransport/Succession.lean).
The chart of N read from a chart of M #
The chart of N read from a chart φ of M through the analytic isomorphism g : N ≃ M and
the linear isomorphism ψ of the models, ψ ∘ φ ∘ g.
Equations
Instances For
chartOfSquare g ψ φ x = ψ (φ (g x)).
The inverse of the read chart is g⁻¹ ∘ φ⁻¹ ∘ ψ⁻¹.
The read chart as a function.
The inverse of the read chart as a function.
The source of the read chart is g⁻¹(φ.source).
The target of the read chart is ψ(φ.target), as a preimage under ψ⁻¹.
A chart of the maximal atlas of M reads as a chart of the maximal atlas of N
(mem_maximalAtlas_of_contMDiffOn: ψ ∘ φ ∘ g and its inverse are analytic on the source and the
target).
Adapted charts, closed submanifolds, the ideal sheaf of a submanifold #
The adapted-chart predicate depends on the chart isomorphism only pointwise.
An adapted chart of M for Y reads as an adapted chart of N for g⁻¹(Y), with the chart
isomorphism ψ.symm.trans ψ₀.
A closed submanifold of M pulls back along g to a closed submanifold of N of the same
codimension.
The adapted chart of M read from an adapted chart of N (the converse direction, through
g⁻¹ and ψ⁻¹).
The coordinate germs along g: the stalk isomorphism of g carries the i-th coordinate germ
of φ to the i-th coordinate germ of ψ ∘ φ ∘ g.
The coordinate germs of equal charts agree.
Reading a chart of N through g⁻¹, ψ⁻¹ and back through g, ψ gives the chart.
The ideal sheaf of a closed submanifold Y pulls back along g to the ideal sheaf of
g⁻¹(Y): the cosupport by cosupport_pullback, the stalks at the points of g⁻¹(Y) because the
coordinate germs of the adapted charts correspond (stalkRingEquiv_coord), each adapted chart of
N being the reading of an adapted chart of M.
The ideal sheaf of a closed submanifold Y of M pulls back along g to the ideal sheaf of
g⁻¹(Y), whatever witnesses of IsClosedSubmanifold the two carry: the pull-back is an ideal
sheaf of g⁻¹(Y) (IsIdealSheafOf.pullbackDiffeomorph), which is unique
(IsIdealSheafOf.eq_idealSheaf) and depends only on the set
(IsClosedSubmanifold.idealSheaf_congr).
Blow-up charts, blowings-up, monoidal transformations along a square #
A blow-up chart of f over the chart of M read from φ' is, read on N' through g' and
ψ, a blow-up chart of f' over φ': the four fields through the square.
A blowing-up [BM88, Definition 4.1] along a square: analyticity, properness
(isProperMap_of_square_iff), the local-isomorphism and bijection clauses off the centre, and the
blow-up charts by IsBlowUpChart.of_square, each chart of N being the reading of a chart of
M.
A monoidal transformation along a square of analytic isomorphisms across the models, with
the model isomorphism ψ, which names the chart isomorphism of N as ψ.symm.trans ψ₀ (without
some E ≃L[𝕜] E' the statement fails when N and N' are empty and E' is not linearly
isomorphic to Fin n → 𝕜). The centre Y pulls back to g⁻¹(Y), its ideal sheaf to the pull-back
of the ideal sheaf, the blowing-up transports by IsBlowUp.of_square.
The Jacobian ideal along a square #
The determinant of the conjugate ψ ∘ A ∘ ψ⁻¹ of an endomorphism A of E by the linear
isomorphism ψ : E ≃L[𝕜] E' is the determinant of A (Mathlib's LinearMap.det_conj through the
coercion to linear maps).
The Jacobian determinant of f' in the charts read from those of f is the Jacobian
determinant of f at the corresponding point: the chart representatives are conjugate by ψ
(det_clm_conj), so the two are equal — no unit germ enters.
The Jacobian stalk along a square: the stalk isomorphism of g' carries the Jacobian stalk of
f at g' b to the Jacobian stalk of f' at b, the generators (the Jacobian determinants in
charts) corresponding by jacobianFun_of_square in the charts read through g, g'. No model
isomorphism is assumed: the inverse differential of g' at b
(Diffeomorph.mfderivToContinuousLinearEquiv) serves as the ψ of the read charts.
The Jacobian ideal [BM97, Theorem 1.10, the sentence after it] along a square of analytic
isomorphisms across the models: stalk by stalk, jacobianStalk_of_square; no model isomorphism
in the statement.