Homotopies of morphisms of right A-infinity modules #
Let f g : M ⟶ N be morphisms of right A∞ modules over a fixed algebra. A homotopy from
f to g is a degree--1 morphism H of their cofree bar comodules satisfying
F - G = b_N H + H b_M.
The comodule morphism H is determined by its suspended Taylor map, obtained by applying the
coalgebra counit. The homotopy equation can likewise be checked after applying the counit. Its
component with no algebra inputs is an ordinary chain homotopy between the linear parts of f
and g; consequently homotopic module morphisms induce the same map on cohomology and are
quasi-isomorphisms together.
Homotopies are reflexive, symmetric, and transitive, and they are preserved by composition with module morphisms on either side.
Main definitions #
TauCeti.AInfinityRightModuleHom.Homotopy: a homotopy of rightA∞module morphisms.TauCeti.AInfinityRightModuleHom.Homotopy.taylor: its suspended Taylor map.TauCeti.AInfinityRightModuleHom.Homotopy.linearHomotopy: its unary component.TauCeti.AInfinityRightModuleHom.Homotopy.ofBarHomotopy: construction from a homogeneous comodule morphism satisfying the suspended component equation.
References #
- B. Keller, Introduction to A-infinity algebras and modules, Section 4.
- K. Lefèvre-Hasegawa, Sur les A-infini catégories, thèse de doctorat, Université Paris 7 (2003), Chapter 1.
A homotopy from f to g is a degree--1 morphism of their cofree bar comodules whose
commutator with the module bar differentials is F - G.
- barHomotopy : Comodule.Hom R (TensorWords R A) (TensorProduct R M (TensorWords R A)) (TensorProduct R N (TensorWords R A))
The degree-
-1morphism of cofree bar comodules. - isHomogeneous_barHomotopy : LinearMap.IsHomogeneous self.barHomotopy.toLinearMap (AInfinityRightModule.barGrading AA MM.grading).piece (AInfinityRightModule.barGrading AA NN.grading).piece (-1)
The bar homotopy lowers the total suspended degree by one.
- barMap_sub_barMap : f.barMap - g.barMap = NN.barDifferential ∘ₗ self.barHomotopy.toLinearMap + self.barHomotopy.toLinearMap ∘ₗ MM.barDifferential
The homotopy equation
F - G = b_N H + H b_M.
Instances For
The underlying linear map of the bar-comodule homotopy.
Equations
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The homotopy equation, applied to one bar-comodule element.
The suspended Taylor map of a module homotopy, obtained by applying the coalgebra counit.
Equations
- h.taylor = ↑(TensorProduct.rid R N) ∘ₗ LinearMap.lTensor N CoalgebraStruct.counit ∘ₗ h.barMap
Instances For
The Taylor map of a homotopy lowers suspended degree by one.
The bar homotopy is the cofree lift of its Taylor map.
Homotopies between fixed morphisms are determined by their Taylor maps.
For a degree--1 comodule morphism, the full homotopy equation is equivalent to its
projection to the cogenerator.
The suspended component equation of a module homotopy.
Construct a homotopy from a degree--1 comodule morphism satisfying the suspended
component equation.
Equations
- TauCeti.AInfinityRightModuleHom.Homotopy.ofBarHomotopy H hH e = { barHomotopy := H, isHomogeneous_barHomotopy := hH, barMap_sub_barMap := ⋯ }
Instances For
The Taylor map of a homotopy constructed from a bar-comodule morphism is its counit component.
The unary component #
The unary component of a module homotopy, evaluated on the empty algebra word.
Equations
- h.linearHomotopy = h.taylor ∘ₗ (TensorProduct.mk R M (TauCeti.TensorWords R A)).flip 1
Instances For
A bar homotopy sends an empty algebra word to the empty word multiplied by its unary component.
The unary component of a module homotopy lowers the unsuspended degree by one.
The unary component is a chain homotopy between the linear parts.
Cohomology #
Homotopic module morphisms induce the same map on unary cohomology.
Homotopic module morphisms are quasi-isomorphisms together.
Equivalence and composition laws #
The zero homotopy from a module morphism to itself.
Equations
- TauCeti.AInfinityRightModuleHom.Homotopy.refl f = { barHomotopy := 0, isHomogeneous_barHomotopy := ⋯, barMap_sub_barMap := ⋯ }
Instances For
Reverse a module homotopy.
Equations
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Concatenate two module homotopies.
Equations
- h.trans h' = { barHomotopy := h.barHomotopy + h'.barHomotopy, isHomogeneous_barHomotopy := ⋯, barMap_sub_barMap := ⋯ }
Instances For
Postcomposition of a homotopy by a module morphism.
Equations
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Postcomposition applies the Taylor map of the outer morphism to the bar homotopy.
Precomposition of a homotopy by a module morphism.
Equations
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Precomposition applies the Taylor map of the homotopy after the inner bar map.