The stratum of a non-singular analytic space is the space of its manifold #
With X_d the stratum of dimension d of a non-singular analytic K-space X, an analytic
manifold by Hironaka.AnalyticSpace.Manifold.Stratum, the comparison morphism Sp(X_d) βΆ X | X_d
(stratumHom) is the identity on points and sends a section s of πͺ_X to the function
y β¦ ev_y(s_y) of its values at the simple points (regEval, Hironaka.AnalyticSpace.RegEval),
which is analytic because through a chart e : (G', π_{G'}) β
X | V it is the chart pullback e^* s composed with the chart (regEval_germ, contMDiff_stratumFun). Its stalk maps are local
(evaluation is preserved, eval_stalkMap_stratumHomAux) and it respects the constants. It is an
isomorphism (isIso_stratumHom, stratumKIso : Sp(X_d) β
X | X_d) because on every chart domain
V_x it agrees, by the extensionality of morphisms between spaces of manifolds on their underlying
maps (hom_ext_baseFun), with the composite of the known isomorphisms
Sp(X_d) | V_x β
Sp(V_x) β
Sp(G'_x) β
X | V_x (stratumCompare_eq), so that its stalk maps are
isomorphisms and the stalk criterion applies.
The three closing theorems state the result in set-theoretic form: isOpen_setOf_ringKrullDim_eq,
iUnion_setOf_ringKrullDim_eq_univ, and exists_manifold_of_isNonsingular, which says that every
stratum of a non-singular analytic space is K-isomorphic to the space of an analytic manifold
modelled on K^d. This is Hironaka's description of the non-singular analytic spaces as those
locally isomorphic to some (G, π_G) [Hir64, Ch. 0, Β§1, p. 121] and BierstoneβMilman's "every
smooth space is a manifold" [BM97, (3.8)(2)]; it is how the manifold-level theorems of the analytic
strand are applied to the non-singular analytic spaces of the analytic-space main theorem.
The image in X of an open of the stratum.
Equations
- X.stratumImage hX d W = β―.functor.obj W
Instances For
The evaluation at a point y of the stratum of the sections over (the image of) an open
W β y of the stratum: s β¦ ev_y(s_y), a ring homomorphism.
Equations
- X.stratumEval hX d W y = (X.regEval β―).comp (CommRingCat.Hom.hom (X.presheaf.germ (X.stratumImage hX d W) ββy β―))
Instances For
The function of a section s of πͺ_X over (the image of) an open W of the stratum:
y β¦ ev_y(s_y).
Equations
- X.stratumFun hX d W s y = (X.stratumEval hX d W y) s
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The chart formula: at the point e_x(q) of the stratum the function of s is the value at q
of the chart pullback of s.
The chart at x writes a point w of V_x as e_x(q), q = e_xβ»ΒΉ(w).
The function of a section is analytic: near x it is the chart pullback of s, an analytic
function on an open subset of K^d, composed with the chart.
The stratum's space of the bundled manifold stratumManifold.
Equations
- X.stratumSpace hX d = AnalyticSpace.KLocallyRingedSpace.ofManifold K (Fin d β K) β₯(X.dimOpens hX d)
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The open subspace X | X_d.
Equations
- X.stratumRestrict hX d = X.restrictOpen (X.dimOpens hX d)
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The sheaf map of the comparison morphism: a section of πͺ_X goes to the function of its
values.
Equations
- One or more equations did not get rendered due to their size.
Instances For
(Implementation.) The morphism of presheafed spaces Sp(X_d) βΆ X | X_d: the identity on points,
evaluation on sections.
Equations
- X.stratumHomAux hX d = { base := CategoryTheory.CategoryStruct.id β(X.stratumSpace hX d).toPresheafedSpace, c := X.stratumSheafHom hX d }
Instances For
The evaluation at a point y of the stratum on the stalk of the open subspace X | X_d.
Equations
- X.stratumRegEval hX d y = (X.regEval β―).comp (CommRingCat.Hom.hom (X.restrictStalkIso β― y).hom)
Instances For
Evaluation is preserved by the comparison morphism.
(Implementation.) The morphism of locally ringed spaces Sp(X_d) βΆ X | X_d.
Equations
- X.stratumHomL hX d = { toHom := X.stratumHomAux hX d, prop := β― }
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The comparison K-morphism Sp(X_d) βΆ X | X_d.
Equations
- X.stratumHom hX d = β¨X.stratumHomL hX d, β―β©
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The comparison morphism is an isomorphism: comparison with Sp(chart) on each chart #
The chart domain V_x β© X_d as an open of the stratum.
Equations
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The restriction of the comparison morphism to a chart domain.
Equations
- One or more equations did not get rendered due to their size.
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The chart domain of X | X_d, read as (G'_x, π_{G'_x}) through the chart.
Equations
- One or more equations did not get rendered due to their size.
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The chart V_x β© X_d β G'_x as a map of the open submanifolds.
Equations
- AnalyticSpace.chartMap x w = (X.chartHomeo hX d x).symm β¨ββw, β―β©
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The inverse chart G'_x β V_x β© X_d.
Equations
- AnalyticSpace.chartMapInv x q = β¨AnalyticSpace.chartPt x q, β―β©
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Sp of the chart, a K-isomorphism Sp(V_x β© X_d) β
Sp(G'_x).
Equations
- AnalyticSpace.chartKIsoM x = AnalyticSpace.KLocallyRingedSpace.ofManifoldIso (AnalyticSpace.chartMap x) (AnalyticSpace.chartMapInv x) β― β― β― β―
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The comparison morphism on the chart domain, read between Sp(V_x β© X_d) and Sp(G'_x).
Equations
- One or more equations did not get rendered due to their size.
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On a chart domain the comparison morphism is Sp of the chart: the two K-morphisms
Sp(V_x β© X_d) βΆ Sp(G'_x) agree on points, hence are equal (hom_ext_baseFun).
The stalk maps of the comparison morphism are isomorphisms: on the chart domain through y
the morphism is Sp of the chart.
The comparison morphism is a K-isomorphism (the stalk criterion; the base map is the
identity).
Sp(X_d) β
X | X_d.
Equations
- X.stratumKIso hX d = CategoryTheory.asIso (X.stratumHom hX d)
Instances For
The strata in set-theoretic form #
The dimension is locally constant on a non-singular space: isOpen_dimSet
(Hironaka.AnalyticSpace.Manifold.Stratum) with dimSet unfolded, the set-theoretic form used in
the statement exists_manifold_of_isNonsingular.
The strata cover a non-singular space: iUnion_dimSet_eq_univ
(Hironaka.AnalyticSpace.Manifold.Stratum) with dimSet unfolded, the set-theoretic form of the
statement.
Every stratum of a non-singular analytic K-space is the space of an analytic manifold
modelled on K^d [Hir64, Ch. 0, Β§1, p. 121], [BM97, (3.8)(2)]: Sp is essentially surjective onto
the non-singular spaces, dimension by dimension. The stratum is quantified as an open set U whose
carrier is the set of points of dimension d, so that the statement does not presuppose the
openness lemma.