Disjoint unions of manifolds as coproducts of analytic spaces #
Consequences of the coproduct construction of Hironaka/AnalyticSpace/Sigma.lean and
Hironaka/AnalyticSpace/SigmaLemmas.lean, and of the disjoint union of analytic manifolds
(sigmaManifold, sigmaMk of Hironaka/Manifold/SigmaManifold.lean), restated here for
reference; nothing but the root aggregator imports this module.
- The coproduct
sigma XinAn/K: its underlyingK-local-ringed space and locally ringed space are the coproducts of the summands', it is Hausdorff and σ-compact, and the cofan(sigma X, sigmaι X)is a colimit cocone (nonempty_isColimit_sigmaCofan). OncehasCoproductis known, Mathlib's∐ Xexists inAn/Kandsigma X ≅ ∐ Xcanonically (IsColimit.coconePointUniqueUpToIso), but not byrfl:∐ Xis aClassical.choice,sigma Xthe explicit construction. - The space of a disjoint union of manifolds is the coproduct of the spaces of the summands
(
toSpace_sigma,toSpace_sigma_hom): in the charts ofΣ i, M i(the charts of theM ilifted along the open embeddingsSigma.mk i) the inclusion of a summand reads as the identity, soSp(Sigma.mk i)is an open immersion, and the descent∐ Sp(M i) ⟶ Sp(Σ i, M i)of these open immersions with disjoint images covering the union is an isomorphism byisIso_sigmaDesc_of_isOpenImmersion(toSpaceSigmaIso, inHironaka/AnalyticSpace/Manifold/). - A non-singular analytic
K-space is the countable disjoint union of pure-dimensional manifolds (nonsingular_eq_sigma_dim): the strataX_d = {x | dim 𝒪_{X,x} = d}are open, pairwise disjoint, coverX, and each isK-isomorphic to the space of a manifold modelled onK^d(stratumManifold,stratumSigmaIso, inHironaka/AnalyticSpace/Manifold/), so the same criterion givesX ≅ ∐ d, Sp(X_d)with the points of local dimensiondthe points of thed-th summand. This exhibits Hironaka's non-singular analyticK-spaces [Hir64, Ch. 0, §1, p. 121] as disjoint unions of manifolds of the several dimensions (the decomposition itself isstratumSigmaIso).
The coproduct in An/K #
theorem
AnalyticSpace.sigma_toLocallyRingedSpace
{K : Type}
[RCLike K]
{ι : Type v}
[Countable ι]
(X : ι → AnalyticSpace K)
:
(sigma X).toLocallyRingedSpace = AlgebraicGeometry.LocallyRingedSpace.coproduct
(KLocallyRingedSpace.coprodDiagram fun (i : ι) => (X i).toKLocallyRingedSpace)
theorem
AnalyticSpace.sigma_t2Space
{K : Type}
[RCLike K]
{ι : Type v}
[Countable ι]
(X : ι → AnalyticSpace K)
:
T2Space ↑↑(sigma X).toPresheafedSpace
theorem
AnalyticSpace.sigma_sigmaCompactSpace
{K : Type}
[RCLike K]
{ι : Type v}
[Countable ι]
(X : ι → AnalyticSpace K)
:
theorem
AnalyticSpace.nonempty_isColimit_sigmaCofan
{K : Type}
[RCLike K]
{ι : Type v}
[Countable ι]
(X : ι → AnalyticSpace K)
:
Disjoint unions of manifolds and the strata of a non-singular space #
theorem
AnalyticSpace.toSpace_sigma
{K : Type}
[RCLike K]
{E : Type u_1}
[NormedAddCommGroup E]
[NormedSpace K E]
{n : ℕ}
(ψ : E ≃L[K] Fin n → K)
{ι : Type u}
[Countable ι]
(M : ι → AnalyticManifold K E)
:
theorem
AnalyticSpace.toSpace_sigma_hom
{K : Type}
[RCLike K]
{E : Type u_1}
[NormedAddCommGroup E]
[NormedSpace K E]
{n : ℕ}
(ψ : E ≃L[K] Fin n → K)
{ι : Type u}
[Countable ι]
(M : ι → AnalyticManifold K E)
:
∃ (e : toSpace ψ (Manifold.sigmaManifold M) ≅ sigma fun (i : ι) => toSpace ψ (M i)),
∀ (i : ι),
CategoryTheory.CategoryStruct.comp (toSpaceHom ψ (Manifold.sigmaMk M i)) e.hom = sigmaι (fun (i : ι) => toSpace ψ (M i)) i
theorem
AnalyticSpace.nonsingular_eq_sigma_dim
{K : Type}
[RCLike K]
(X : AnalyticSpace K)
(hX : X.IsNonsingular)
:
∃ (M : (d : ℕ) → AnalyticManifold K (Fin d → K)) (e :
X ≅ sigma fun (d : ℕ) => toSpace (ContinuousLinearEquiv.refl K (Fin d → K)) (M d)),
∀ (d : ℕ) (x : ↑↑X.toPresheafedSpace),
ringKrullDim ↑(X.presheaf.stalk x) = ↑d ↔ ∃ (m : (M d).carrier),
↑e.hom x = ↑(sigmaι (fun (d : ℕ) => toSpace (ContinuousLinearEquiv.refl K (Fin d → K)) (M d)) d) m