Mapping cones of curved differential graded right modules #
The cone of a closed map f : M ⟶ N has underlying graded right module M[1] × N and
differential (x, y) ↦ (-dM x, f x + dN y). The two off-diagonal terms in its square cancel
because f commutes with the differentials. Its curvature is therefore the same as the
curvature of M and N, without a centrality assumption.
The right action is unchanged. The canonical inclusion of N and projection to M[1] are
closed maps, and the adjacent composites vanish in the existing homotopy category. A closed map
g : N ⟶ P with f ≫ g = 0 induces the closed map coneDesc f g hfg : cone(f) ⟶ P.
A null-homotopic closed map factors through its source's identity cone via the inclusion.
References #
- L. Positselski, Differential graded Koszul duality: an introductory survey, Sections 6.2 and 7.6. His curvature is the negative of the right-module curvature stored here.
- The Tau Ceti contributors,
TauCeti.Algebra.Homology.Curved.Cone.Basic: the curved-duplex cone formalization is the precedent for the cone, its maps and its contraction interface. - The Tau Ceti contributors,
TauCeti.Algebra.Homology.Curved.Frobenius: the identity-cone factorization adapts the corresponding componentwise split construction.
The cone differential uses the linear mapping-cone construction on the ground-ring maps.
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The cone differential has diagonal entries -dM and dN and lower-left entry f.
The cone of a closed map, with grading M[1] × N and the original curvature.
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The degree-p part of the cone is Mᵖ⁺¹ × Nᵖ.
The differential on the cone acts by the usual block formula.
The closed inclusion of the codomain into its cone.
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The closed projection from the cone to the cohomological shift of its domain.
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The cone inclusion is the usual second linear inclusion.
The cone projection is the usual first linear projection.
The inclusion followed by the projection vanishes already in the closed category.
The inclusion followed by the projection vanishes already in the closed category.
A closed map g killing the closed map f induces the closed map cone(f) ⟶ P
sending (x, y) to g y.
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The map out of the cone applies g to the second component.
The cone inclusion followed by the induced map out of the cone is the original map.
The cone inclusion followed by the induced map out of the cone is the original map.
The first linear inclusion, viewed as a degree-minus-one homotopy into the cone.
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The homotopy for the first adjacent composite sends x to (x, 0).
The first adjacent composite is the boundary of the first inclusion homotopy.
The second projection, viewed as a degree-minus-one homotopy to the shifted codomain.
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The homotopy for the third adjacent composite sends (x, y) to y.
The projection followed by the shifted map is the boundary of the second projection.
The first adjacent composite vanishes in the curved homotopy category.
The first adjacent composite vanishes in the curved homotopy category.
The third adjacent composite also vanishes in the curved homotopy category.
The third adjacent composite also vanishes in the curved homotopy category.
The contracting homotopy of the cone of an isomorphism applies its inverse to the second component and includes the result into the first component.
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The contraction sends (x, y) to (f⁻¹ y, 0).
A corrected degree-minus-one cochain for a closed map g and cochains α, β.
For t = f ∘ α - β ∘ f, its matrix is (α - g ∘ t, g; β ∘ t, -β).
It is a contraction when the inverse-homotopy equations in
coneHomotopyContraction_boundary hold.
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The corrected degree-minus-one cochain has this block formula on the cone carrier.
Inverse homotopies make the corrected contraction a boundary of the identity.
The correction uses the closed odd map t = f ∘ α - β ∘ f, so no coherence between the
chosen inverse homotopies, or zero-curvature hypothesis, is required.
A closed map which becomes an isomorphism in the homotopy category has a contractible cone.
The strict inverse contraction is the zero-homotopy case of the corrected contraction.
The strict contraction boundary follows from the general inverse-homotopy formula.
A square commuting up to the specified odd homotopy induces a closed map of cones.
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The underlying cone map has the homotopy as its lower-left entry.
A cone map sends (x, y) to (a x, b y + k x).
Cone maps commute with the canonical inclusions.
Cone maps commute with the canonical inclusions.
Cone maps commute with the canonical projections and the shifted domain map.
Cone maps commute with the canonical projections and the shifted domain map.
The homotopy for a composite of two cone-map squares is b' ∘ k + k' ∘ a.
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The composite square homotopy evaluates by post- and precomposition.
The sum of the two square homotopies witnesses the composite square.
Cone maps compose using the induced composite square homotopy.
Cone maps compose using the induced composite square homotopy.
The cone map of the identity square with zero homotopy is the identity.
A closed map is null-homotopic exactly when it factors through the identity cone of its source via the canonical inclusion.