Basic exterior powers of sheaves of modules #
Given a site (C, J) carrying a sheaf of commutative rings R and n : ℕ, the n-th exterior
power of a sheaf of R-modules M is obtained by taking sectionwise exterior powers
⋀[R(U)]^n M(U) (PresheafOfModulesOfCommRing.exteriorPower) and sheafifying, exactly as
the tensor product TauCeti.SheafOfModules.tensorProduct sheafifies sectionwise tensor products.
On a scheme X this gives SheafOfModules.exteriorPower X.sheaf n : X.Modules ⥤ X.Modules, the
exterior powers of 𝒪ₓ-modules from which determinants of vector bundles are built.
Main declarations #
SheafOfModules.exteriorPower R nis then-th exterior power, as an endofunctor of sheaves ofR-modules;SheafOfModules.exteriorPowerIsoandSheafOfModules.exteriorPower_mapare its defining identification with the sheafification of the sectionwise exterior power;SheafOfModules.exteriorPowerZeroIsoidentifies⋀⁰ Mwith the structure sheaf;SheafOfModules.exteriorPowerOneIsoidentifies⋀¹ MwithM;SheafOfModules.presheafPushforwardExteriorPowerIsoidentifies the exterior power of the pushforward of a presheaf of modules with the pushforward of its exterior power;SheafOfModules.pushforwardExteriorPowerIsoidentifies the pushforward of⋀ⁿ Malong a continuous and cocontinuous functor with the exterior power of the pushforward ofM, andSheafOfModules.overExteriorPowerIsospecializes it to the restriction(⋀ⁿ M)|_X ≅ ⋀ⁿ (M|_X)to a slice site; both are natural inM(pushforwardExteriorPowerIso_hom_naturality,overExteriorPowerIso_hom_naturality).
The restriction comparison lets local computations of exterior powers, such as those on the charts of a locally free sheaf, be carried out on the restriction to a covering object.
The n-th exterior power of sheaves of R-modules: the sectionwise exterior power of the
underlying presheaf of modules, sheafified.
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The defining identification of the exterior power of a sheaf of modules with the sheafification of the sectionwise exterior power of its underlying presheaf of modules.
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The exterior power of a morphism of sheaves of modules is the sheafification of the sectionwise exterior power of the underlying morphism of presheaves of modules.
The zeroth exterior power of a sheaf of modules is the structure sheaf, naturally.
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The first exterior power of a sheaf of modules is the sheaf itself, naturally.
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On components, exteriorPowerZeroIso is the sheafification of the presheaf-level
identification PresheafOfModulesOfCommRing.exteriorPowerZeroIso, followed by the identification of
the sheafified unit with the structure sheaf.
On components, exteriorPowerZeroIso is the sheafification of the presheaf-level
identification PresheafOfModulesOfCommRing.exteriorPowerZeroIso, followed by the identification of
the sheafified unit with the structure sheaf.
On components, exteriorPowerOneIso is the sheafification of the presheaf-level
identification PresheafOfModulesOfCommRing.exteriorPowerOneIso, followed by the counit
TauCeti.SheafOfModules.sheafificationIso.
On components, exteriorPowerOneIso is the sheafification of the presheaf-level
identification PresheafOfModulesOfCommRing.exteriorPowerOneIso, followed by the counit
TauCeti.SheafOfModules.sheafificationIso.
Exterior powers of presheaves of modules commute with the pushforward of presheaves of modules
underlying pushforwardModule F R: over X, both sides have sections ⋀[R(F X)]^n M(F X) and
the same restriction maps.
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On sections, presheafPushforwardExteriorPowerIso is the identity of ⋀[R(F X)]^n M(F X).
On sections, the inverse of presheafPushforwardExteriorPowerIso is the identity of
⋀[R(F X)]^n M(F X).
For each sheaf of modules M, pushforward along a continuous and cocontinuous functor
commutes with the n-th exterior power: F_*(⋀ⁿ M) ≅ ⋀ⁿ (F_* M).
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The forward map of pushforwardExteriorPowerIso is the sheafification--pushforward comparison
followed by the sheafified presheaf-level comparison presheafPushforwardExteriorPowerIso, read
through the defining identifications of the two exterior powers.
pushforwardExteriorPowerIso is natural in the sheaf of modules.
pushforwardExteriorPowerIso is natural in the sheaf of modules.
For each object X of the site, the restriction of ⋀ⁿ M to the slice site over X is the
n-th exterior power of the restriction of M.
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The forward map of overExteriorPowerIso is the slice-site instance of
pushforwardExteriorPowerIso_hom.
overExteriorPowerIso is natural in the sheaf of modules.
overExteriorPowerIso is natural in the sheaf of modules.