Closed embeddings of analytic manifolds #
A closed embedding τ : N → M of analytic manifolds
(AnalyticManifold.IsClosedAnalyticEmbedding: an analytic embedding, Mathlib's
IsSmoothEmbedding at ω, with closed image — the first two clauses of
IdealSheaf.IsPushforwardAlong, IdealSheaf.IsPushforwardAlong.isClosedAnalyticEmbedding) has
the universal property of the subspace τ(N): every analytic map
into M with values in τ(N) factors analytically through τ
(IsClosedAnalyticEmbedding.exists_comp_eq). When its image is a closed submanifold it identifies
N with the bundled submanifold IsClosedSubmanifold.toAnalyticManifold of its image
(IsClosedAnalyticEmbedding.toDiffeomorph): the corestriction of τ is analytic into the bundled
submanifold, and its inverse is the factorization of the inclusion of the submanifold through τ.
Conversely a closed embedding of the spaces onto a closed submanifold, through which the inclusion
of the submanifold factors analytically, is an immersion, so a closed embedding of analytic
manifolds (IsClosedAnalyticEmbedding.of_isClosedSubmanifold, through the splitting splitEquiv
of the coordinates along the adapted indices); so the push-forward of ideal sheaves may equally be
stated with the universal property (IdealSheaf.isPushforwardAlong_iff_exists_comp_eq). The
dimensions of two analytically isomorphic nonempty manifolds agree (dim_eq_of_diffeomorph: the
differential at a point is a linear isomorphism of the models).
The re-modelling of τ between manifolds on different model spaces (transportBetween, the
two-model form of AnalyticMap.transport) keeps the closed embedding onto a closed submanifold
(IsClosedAnalyticEmbedding.transportBetween), the closed submanifold τ(N) with its codimension
(IsClosedSubmanifold.range_transportBetween), the containment of its ideal sheaf in an ideal
sheaf (stalkIdeal_idealSheaf_range_transportBetween_le) and the pull-back of ideal sheaves
along τ (IdealSheaf.transport_pullback_transportBetween); these carry the hypotheses of the
commutation of a principalization with closed embeddings to the standard models. The restriction
of τ between opens U' ⊆ N, U ⊆ M with τ(U') ⊆ U is restrictBetween.
The coordinates of 𝕜ⁿ split into those outside the range of σ and those on it.
Equations
- Manifold.splitCoordₗ σ = { toFun := fun (y : Fin n → 𝕜) => (Manifold.projCompl σ y, fun (i : Fin s) => y (σ i)), map_add' := ⋯, map_smul' := ⋯ }
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The linear isomorphism 𝕜^{n-s} × 𝕜^s ≃ E of the coordinates ψ split along σ: it sends
(w, 0) to the point of the coordinate subspace {z_σ = 0} with the other coordinates w
(splitEquiv_apply_zero).
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The analytic map τ : N → M, between analytic manifolds modelled on E' and on E, is a
closed embedding of analytic manifolds: an analytic embedding (Mathlib's IsSmoothEmbedding at
ω: an analytic immersion, of the form u ↦ (u, 0) in suitable charts near every point, which is a
homeomorphism onto its image) with closed image.
Equations
- AnalyticManifold.IsClosedAnalyticEmbedding τ = (Manifold.IsSmoothEmbedding (modelWithCornersSelf 𝕜 E') (modelWithCornersSelf 𝕜 E) ⊤ ⇑τ ∧ IsClosed (Set.range ⇑τ))
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The factorization through a closed embedding #
A closed embedding of analytic manifolds is a closed embedding of the underlying spaces.
Every analytic map into M with values in τ(N) factors analytically through τ: the
factor is continuous since τ is a topological embedding, and analytic since τ is an analytic
immersion (ContMDiff.iff_comp_isImmersion).
The image of a closed embedding of analytic manifolds is a closed submanifold, for a
finite-dimensional model E of M, in the coordinates ψ : E ≃ 𝕜ⁿ of any basis, of codimension
the dimension s of the complement of the immersion. At τ x, in the charts c of N and d of
M in which τ reads u ↦ ε(u, 0) (ε : E' × F ≃ E), the chart d read through the linear
automorphism ψ⁻¹ ∘ A ∘ ε⁻¹ of E, with A : E' × F ≃ 𝕜ⁿ sending F onto the last s
coordinates, and restricted to the open set where ε⁻¹ ∘ d has its first component in the target
of c and over which the image of the source of c is the trace of τ(N) (τ being a
topological embedding), is adapted to τ(N).
The identification of N with the bundled submanifold τ(N) #
The range of the inclusion of the bundled submanifold τ(N) lies in the range of τ.
An injective analytic map τ with an analytic section h' : τ(N) → N over the inclusion of the
bundled closed submanifold τ(N) is an analytic isomorphism of N with τ(N): the corestriction
of τ, analytic into the bundled submanifold (IsClosedSubmanifold.contMDiff_codRestrict), with
inverse h'.
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The factorization of the inclusion of the bundled submanifold τ(N) through τ, an analytic
map τ(N) → N (IsClosedAnalyticEmbedding.exists_comp_eq).
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τ after the factorization is the inclusion of the submanifold.
The closed embedding τ as an analytic isomorphism of N with the bundled closed
submanifold τ(N) (diffeomorphOfSection), with inverse the factorization of the inclusion
through τ (IsClosedAnalyticEmbedding.ofSub).
Equations
- hτ.toDiffeomorph hS = AnalyticManifold.diffeomorphOfSection hS ⋯ (hτ.ofSub hS) ⋯
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The isomorphism is τ on points.
An analytic map identified with the inclusion of a closed submanifold of its image is an
immersion: if an analytic isomorphism e : N ≃ τ(N) onto the bundled closed submanifold τ(N)
of codimension s is τ on points, then τ is an analytic immersion with complement 𝕜^s. At
x, with the adapted chart φ (indices σ) of the chosen chart of τ(N) at e x and the
differential L : 𝕜^{n-s} ≃ E' of e⁻¹ at e x, τ reads u ↦ ψ⁻¹(embedCompl σ (L⁻¹ u)) in the
chart L ∘ chartAt ∘ e of N and the chart φ of M, a linear map u ↦ (u, 0) up to the
splitting splitEquiv ψ σ of the coordinates.
A closed embedding of the spaces whose image is a closed submanifold, through which the
inclusion of the submanifold factors analytically, is a closed embedding of analytic manifolds:
the factorization identifies N with the bundled submanifold (diffeomorphOfSection), so τ is
an immersion (isImmersionOfComplement_of_diffeomorph).
The push-forward of ideal sheaves through a closed submanifold #
Along a push-forward of ideal sheaves, τ is a closed embedding of analytic manifolds.
The ideal sheaf of the closed submanifold τ(N), in any coordinates, lies in I when the ideal
of τ(N) does: its stalks are the vanishing ideals
(IsClosedSubmanifold.stalkIdeal_idealSheaf_eq_vanishingStalk).
For a finite-dimensional model E of M, the image of τ is a closed submanifold whose ideal
sheaf lies in I (IsClosedAnalyticEmbedding.exists_isClosedSubmanifold).
The push-forward of ideal sheaves through the closed submanifold and the universal property
of the embedding, for a finite-dimensional model E of M: I.IsPushforwardAlong J τ holds
exactly when τ is a closed embedding of the spaces through which every analytic map into M
with values in τ(N) factors analytically, τ(N) is a closed submanifold whose ideal sheaf lies in
I, and J = τ^*I. Given the closed submanifold, the factorization of its inclusion makes τ an
immersion (IsClosedAnalyticEmbedding.of_isClosedSubmanifold), and the stalks of its ideal sheaf
are the vanishing ideals; conversely a closed embedding of analytic manifolds has the universal
property (IsClosedAnalyticEmbedding.exists_comp_eq) and its image is a closed submanifold
(IsClosedAnalyticEmbedding.exists_isClosedSubmanifold).
The dimensions of isomorphic manifolds #
Two analytically isomorphic manifolds modelled on 𝕜^m and 𝕜^k, one of them nonempty, have
m = k: the differential of the isomorphism at a point is a linear isomorphism of the models.
The restriction of τ between opens #
The restriction U' → U of an analytic map τ : N → M to opens with τ(U') ⊆ U.
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The restriction is τ on points.
The re-modelling of τ #
An analytic map τ : N → M read between the re-modelled manifolds N.transport ψ' and
M.transport ψ, for two model changes: the same map on points (the two-model form of
AnalyticMap.transport).
Equations
- AnalyticManifold.transportBetween ψ ψ' τ = ⟨fun (x : (N.transport ψ').carrier) => M.toTransport ψ (τ (N.ofTransport ψ' x)), ⋯⟩
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The re-modelled map is the map on points.
The range of the re-modelled map is the preimage of the range of τ under the identity
M.transport ψ → M.
The range of the re-modelled map is a closed submanifold of the re-modelled M of the same
codimension, for the chart read through ψ (IsClosedSubmanifold.preimage_of_square along the
identity M.transport ψ → M).
The re-modelled map of a closed embedding of analytic manifolds whose image is a closed
submanifold is a closed embedding: the same map of the same spaces, whose image is the closed
submanifold IsClosedSubmanifold.range_transportBetween, through which the inclusion of that
submanifold factors (through τ, after the identity M.transport ψ → M;
IsClosedAnalyticEmbedding.of_isClosedSubmanifold).
The containment of the ideal sheaf of τ(N) in an ideal sheaf I, stalk by stalk, carries to
the re-modelled manifold (IsClosedSubmanifold.idealSheaf_pullbackDiffeomorph).
The re-modelled pull-back of an ideal sheaf along τ is the pull-back of the re-modelled ideal
sheaf along the re-modelled map (both are the pull-back along the same map on points).