The graded module of the coinduced resolution #
The shifted canonical resolution has degree-n term C(G, …, C(G, X)), with n + 1
function-space layers. Its external direct sum carries the canonical square-zero differential
of degree one and the componentwise G-action. The augmentation includes X as constant
functions in degree zero. A compatible pair, a continuous homomorphism φ : H →ₜ* G with a
morphism f : res φ X ⟶ Y, acts degreewise through Mathlib's resolution maps F ↦ f ∘ F ∘ φ;
coefficient morphisms are the case φ = id. This change of group is how restriction and
inflation reach cocycles written on the total module.
For a compact group, a discrete scalar ring R, and smooth discrete coefficients, the total
module with its discrete topology is again smooth. This provides a graded coefficient module for
finite tensor induction of resolutions; tensor products can apply the differential on one carrier
while tracking its degree.
Evaluation at 1 contracts the total module onto the coefficients. The projection π evaluates
the degree-zero component at 1, and the homotopy h, of degree minus one, is the total map of
the contraction TopRep.resolutionModuleHomotopy of the underlying complex. Together with the
augmentation ι they satisfy π ∘ ι = 1 and d ∘ h + h ∘ d = 1 - ι ∘ π. Neither π nor h is
equivariant. Being linear data on one carrier, this contraction can be tensored factor by factor
to contract a tensor power of total resolutions onto the tensor power of the coefficients.
Main results #
gradedResolutionTopRepDifferentialbundles the square-zero differential as a morphism of discrete topological representations.gradedResolutionTopRepAugmentationincludes discrete coefficients into the degree-zero term as a morphism of topological representations, naturally in the coefficients.gradedResolutionMapis the map of a compatible pair; it commutes with the differentials, the augmentations, the projections and the contracting homotopies, preserves degrees, and composes along composite pairs.gradedResolutionTopRepMapbundles coefficient maps, preserving identities, composition, and the differential.gradedResolutionTopRepResMapbundles the map of a compatible pair as a morphism from the restricted total resolution, of degree zero and commuting with the differentials and the augmentations.TauCeti.smoothGradedResolutionFunctorpackages the smooth total resolution functorially.TauCeti.smoothGradedResolutionAugmentationis its natural coefficient augmentation, andTauCeti.smoothGradedResolutionDifferentialits differential.TauCeti.smoothGradedResolutionResMapcompares the restriction of the smooth total resolution along a continuous homomorphism with the smooth total resolution of the restriction.gradedResolutionProjectionandgradedResolutionHomotopycontract the total resolution:gradedResolutionProjection_augmentationandgradedResolutionDifferential_gradedResolutionHomotopy_addare the contraction identities, and both maps are natural in the coefficients;gradedResolutionProjection_eq_zero_of_memandgradedResolutionHomotopy_eq_zero_of_mem_zerosay that they vanish in nonzero and in zero degree.gradedResolutionModule_add_self_eq_zero: the total resolution of coefficients that are their own additive inverses has the same property.
References #
- L. Evens, A generalization of the transfer map in the cohomology of groups, Transactions of the American Mathematical Society 108 (1963), §§2–5.
- Mathlib's
TopRep.resolution',ContinuousCohomology.resolutionMap, andRepresentation.directSumsupply the resolution, coefficient maps, and total action.
The direct sum of the shifted coinduced resolution. Degree zero is C(G, X).
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The componentwise scalar action on the total resolution. Open this scope when tensoring resolutions: for integer scalars, the fallback action on the underlying additive group need not be definitionally equal to this direct-sum action.
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The canonical differential on the total shifted resolution.
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On degree n, the total differential is the original resolution differential d (n + 1).
The differential of the total shifted resolution squares to zero.
If every coefficient is its own additive inverse, then so is every element of the total resolution.
The integer homogeneous-piece family of the total resolution, zero in negative degrees.
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The homogeneous resolution terms decompose the total resolution as an internal direct sum.
In a nonnegative degree, the homogeneous piece is the corresponding resolution term's copy.
The total resolution has no negative homogeneous pieces.
Inclusion of a resolution term gives an element in its homogeneous degree.
The total resolution differential has degree one.
The componentwise group representation on the total shifted coinduced resolution.
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The group action on an included term is its original resolution action.
The degree-n component of g • v is g applied to the degree-n component of v.
The total resolution differential is equivariant.
The componentwise action preserves the homogeneous pieces.
The augmentation of X into the degree-zero term of the total shifted resolution.
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The augmentation includes the constant resolution element in degree zero.
The augmentation takes values in degree zero.
The augmentation takes values in the kernel of the differential.
The augmentation is equivariant for the original action on X.
The augmentation embeds the coefficient module.
The map of the total shifted resolutions induced by a compatible pair: a continuous
homomorphism φ : H →ₜ* G and a morphism f : res φ X ⟶ Y. It is Mathlib's
ContinuousCohomology.resolutionMap φ f, F ↦ f ∘ F ∘ φ, in every degree. At φ = id it is
the map induced by a coefficient morphism.
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The map of a compatible pair acts on an included term by Mathlib's resolution map.
The map of a compatible pair commutes with the total differentials.
The map of a compatible pair carries cocycles to cocycles.
The map of a compatible pair carries the augmentation of x to the augmentation of
f x.
The map of a compatible pair preserves the homogeneous degrees of the total resolutions.
The map of a compatible pair preserves each homogeneous piece of the total resolution.
The map of a compatible pair intertwines the action of φ h on the total resolution of X
with the action of h on that of Y.
The map of a compatible pair carries invariant elements to invariant elements.
Identity coefficients induce the identity on the total resolution.
The maps of compatible pairs compose on the total resolutions.
The projection of the total shifted resolution onto its coefficients: evaluation at 1 of
the degree-zero component. It retracts the augmentation, but it is not equivariant.
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The projection evaluates a degree-zero term at 1.
The projection vanishes on the positive-degree terms.
The projection retracts the augmentation.
The contracting homotopy of the total shifted resolution: it lowers the degree by one,
evaluating the outermost variable of a positive-degree term at 1, and vanishes in degree
zero. It is the total map of TopRep.resolutionModuleHomotopy, and it is not equivariant.
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The contracting homotopy vanishes in degree zero.
In positive degree, the contracting homotopy evaluates the outermost variable at 1.
The contracting homotopy vanishes on the augmentation.
The projection vanishes on the image of the total differential.
The contraction identity of the total shifted resolution:
d ∘ h + h ∘ d = 1 - ι ∘ π, for the augmentation ι and the projection π.
The contracting homotopy of the total shifted resolution has degree minus one.
The projection vanishes on every homogeneous piece of nonzero degree.
The contracting homotopy vanishes on the homogeneous piece of degree zero.
The projection is natural in compatible pairs: evaluation at 1 commutes with
F ↦ f ∘ F ∘ φ because φ 1 = 1.
The contracting homotopy is natural in compatible pairs: evaluating the outermost variable
at 1 commutes with F ↦ f ∘ F ∘ φ because φ 1 = 1.
The total resolution with its discrete topology and componentwise group action.
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The bundled discrete representation retains the total resolution carrier.
The bundled action is the componentwise resolution action.
The bundled discrete action on an included term is the original resolution action.
The bundled discrete action preserves the homogeneous pieces.
The total resolution carries the discrete topology.
The total resolution differential as a morphism of discrete topological representations.
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Bundling the total differential preserves its action on the original direct-sum carrier.
The bundled total differential has degree one.
The differential of the bundled discrete resolution squares to zero.
The augmentation from discrete coefficients into the total resolution as a morphism of topological representations.
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Bundling the augmentation preserves its action on the original coefficient carrier.
The bundled augmentation takes values in the kernel of the total differential.
Change of group on the total resolution. A compatible pair, a continuous homomorphism
φ : H →ₜ* G and a morphism f : res φ X ⟶ Y', induces a morphism from the restriction along φ
of the discrete total resolution of X to that of Y', given by F ↦ f ∘ F ∘ φ in every
degree. It has degree zero and commutes with the differentials and the augmentations.
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The change-of-group morphism acts on the total resolution by gradedResolutionMap.
The change-of-group morphism preserves the homogeneous degrees of the total resolutions.
The change-of-group morphism commutes with the total differentials.
The change-of-group morphism lies over f: it carries the augmentation of the restricted
coefficients to the augmentation of Y'.
Change-of-group morphisms of total resolutions compose along composite compatible pairs.
A coefficient morphism induces a morphism of discrete total resolutions.
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Bundling a coefficient map preserves its action on the original direct-sum carrier.
Identity coefficients induce the identity morphism of the discrete total resolution.
Bundled coefficient maps preserve composition.
Bundled coefficient maps commute with the resolution differential.
Bundled coefficient maps preserve the augmentations of discrete coefficients.
For a compact group, a discrete scalar ring R, and smooth discrete coefficients, the total
coinduced resolution is smooth: each element has finitely many components, whose open
stabilizers have open intersection.
The total shifted coinduced resolution, as a functor on smooth discrete coefficient representations.
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The smooth total-resolution functor sends a coefficient object to its total shifted coinduced resolution.
This is not a simp lemma: rewriting the objects would take the morphism-evaluation lemmas, such as
smoothGradedResolutionAugmentationApp_hom_apply, out of simp-normal form.
The action on the object of the smooth total-resolution functor is the action on the total shifted coinduced resolution.
The smooth total-resolution functor acts on morphisms by the induced map of total resolutions.
The coefficient augmentation into the total shifted coinduced resolution.
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The coefficient augmentations into the total shifted coinduced resolution are natural among smooth discrete coefficient representations.
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The component of the smooth total-resolution augmentation is the named augmentation.
The smooth total-resolution augmentation acts by the ordinary augmentation on carriers.
The differential of the total shifted coinduced resolution, as an endomorphism of the smooth total resolution.
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The smooth total-resolution differential acts by the ordinary total differential on carriers.
Restriction of the smooth total resolution. The restriction along a continuous
homomorphism φ : H →* G of the total resolution of A, compared with the total resolution of
the restriction of A: it pulls back cochains along φ (TopRep.gradedResolutionTopRepResMap).
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The restriction of the smooth total resolution pulls back cochains along φ.
The restriction of the smooth total resolution preserves degrees.
The restriction of the smooth total resolution commutes with the total differentials.
The restriction of the smooth total resolution commutes with the augmentations.