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DerivedAlgGeo.CategoryTheory.Triangulated.FourierMukai.AdjunctionUnitKernel

Kernel realizations of adjunction units #

Let Φ_P : X ⥤ Y have a kernel-presented right adjoint Φ_Q. With a convolution kernel and a diagonal unit kernel on X, the adjunction unit has the form

Φ_{O_Δ} ⟶ Φ_{conv P Q}.

Here conv P Q presents Φ_P ⋙ Φ_Q. The abbreviations AdjunctionUnitKernelData and AdjunctionUnitKernelConeData specialize the generic kernel-transformation interfaces to an ordinary kernel morphism O_Δ ⟶ conv P Q, its enhanced representative, and a chosen dg cone. They are abbreviations rather than parallel records, since there is no legacy unit realization API to preserve.

Exactness in the kernel variable gives a source-natural, pointwise distinguished unshifted unit triangle

𝟭 X ⟶ Φ_P ⋙ Φ_Q ⟶ cotwistCone ⟶ (𝟭 X)⟦1⟧.

The third functor is the unshifted cotwist-cone candidate. Its pointwise [-1] shift is the conventional, choice-dependent ordinary cotwist, and inverse rotation gives the source-natural triangle

cotwist ⟶ 𝟭 X ⟶ Φ_P ⋙ Φ_Q ⟶ cotwist⟦1⟧.

The shift and inverse rotation reuse the functor-category HasShift instance and Mathlib's invRotate; no signed map is reconstructed here. The existing shift comparison of a shift-coherent kernel family presents the cotwist by the cone kernel shifted inside the enhancement's homotopy category. No representative or cone is canonical, and no exactness, autoequivalence, or sphericality claim is made.

AdjunctionUnitKernelData.ofFull is only a sufficient abstract constructor. Without the explicit fullness hypothesis, producing the kernel arrow remains the geometric unit-realization obligation.

@[reducible, inline]
abbrev CategoryTheory.Triangulated.FourierMukai.AdjunctionUnitKernelData {X : Type uX} {Y : Type uY} {W₁ : Type u₁} {W₂ : Type u₂} {W : Type uW} [Category.{vX, uX} X] [Category.{vY, uY} Y] [Category.{v₁, u₁} W₁] [Category.{v₂, u₂} W₂] [Category.{vW, uW} W] (C : Correspondence X Y W₁) (C' : Correspondence Y X W₂) (E : Correspondence X X W) (P : W₁) (R : RightAdjointKernelData C C' P) (D : ConvolutionData C C' E) (U : UnitKernelData E) :
Type vW

An ordinary kernel arrow realizing the unit of a kernel-presented right adjunction. This is a definitional specialization of the generic kernel-transformation interface.

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    @[reducible, inline]
    abbrev CategoryTheory.Triangulated.FourierMukai.AdjunctionUnitKernelConeData {X : Type uX} {Y : Type uY} {W₁ : Type u₁} {W₂ : Type u₂} {W : Type uW} [Category.{vX, uX} X] [Category.{vY, uY} Y] [Category.{v₁, u₁} W₁] [Category.{v₂, u₂} W₂] [Category.{vW, uW} W] (C : Correspondence X Y W₁) (C' : Correspondence Y X W₂) (E : Correspondence X X W) (e : Enhancement W) (P : W₁) (R : RightAdjointKernelData C C' P) (D : ConvolutionData C C' E) (U : UnitKernelData E) :
    Type (max uE vE)

    An enhanced representative and chosen dg cone of a kernel arrow realizing the unit of a kernel-presented right adjunction.

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      The specialized kernel-transform equation for the adjunction unit.

      noncomputable def CategoryTheory.Triangulated.FourierMukai.AdjunctionUnitKernelData.ofFull {X : Type uX} {Y : Type uY} {W₁ : Type u₁} {W₂ : Type u₂} {W : Type uW} [Category.{vX, uX} X] [Category.{vY, uY} Y] [Category.{v₁, u₁} W₁] [Category.{v₂, u₂} W₂] [Category.{vW, uW} W] {C : Correspondence X Y W₁} {C' : Correspondence Y X W₂} {E : Correspondence X X W} {P : W₁} {R : RightAdjointKernelData C C' P} {D : ConvolutionData C C' E} {U : UnitKernelData E} [E.kernelTransform.Full] :

      Fullness of the kernel transform is sufficient to realize the adjunction unit by an ordinary kernel morphism.

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        noncomputable def CategoryTheory.Triangulated.FourierMukai.AdjunctionUnitKernelData.toConeData {X : Type uX} {Y : Type uY} {W₁ : Type u₁} {W₂ : Type u₂} {W : Type uW} [Category.{vX, uX} X] [Category.{vY, uY} Y] [Category.{v₁, u₁} W₁] [Category.{v₂, u₂} W₂] [Category.{vW, uW} W] {C : Correspondence X Y W₁} {C' : Correspondence Y X W₂} {E : Correspondence X X W} {P : W₁} {R : RightAdjointKernelData C C' P} {D : ConvolutionData C C' E} {U : UnitKernelData E} (S : AdjunctionUnitKernelData C C' E P R D U) (e : Enhancement W) :

        Choose a closed representative and dg cone for the unit-kernel arrow. Both choices are noncanonical.

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          @[reducible, inline]
          abbrev CategoryTheory.Triangulated.FourierMukai.AdjunctionUnitKernelConeData.cotwistCone {X : Type uX} {Y : Type uY} {W₁ : Type u₁} {W₂ : Type u₂} {W : Type uW} [Category.{vX, uX} X] [Category.{vY, uY} Y] [Category.{v₁, u₁} W₁] [Category.{v₂, u₂} W₂] [Category.{vW, uW} W] {C : Correspondence X Y W₁} {C' : Correspondence Y X W₂} {E : Correspondence X X W} {e : Enhancement W} {P : W₁} {R : RightAdjointKernelData C C' P} {D : ConvolutionData C C' E} {U : UnitKernelData E} (S : AdjunctionUnitKernelConeData C C' E e P R D U) :

          The transform of the selected cone: the unshifted cotwist-cone candidate.

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            @[reducible, inline]
            noncomputable abbrev CategoryTheory.Triangulated.FourierMukai.AdjunctionUnitKernelConeData.cotwist {X : Type uX} {Y : Type uY} {W₁ : Type u₁} {W₂ : Type u₂} {W : Type uW} [Category.{vX, uX} X] [Category.{vY, uY} Y] [Category.{v₁, u₁} W₁] [Category.{v₂, u₂} W₂] [Category.{vW, uW} W] {C : Correspondence X Y W₁} {C' : Correspondence Y X W₂} {E : Correspondence X X W} {e : Enhancement W} {P : W₁} {R : RightAdjointKernelData C C' P} {D : ConvolutionData C C' E} {U : UnitKernelData E} (S : AdjunctionUnitKernelConeData C C' E e P R D U) [HasShift X ℤ] :

            The conventional, choice-dependent ordinary cotwist: the pointwise [-1] shift of the selected cotwist-cone transform. This is a functor only; no exactness or equivalence is asserted.

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              @[reducible, inline]
              noncomputable abbrev CategoryTheory.Triangulated.FourierMukai.AdjunctionUnitKernelConeData.cotwistKernel {X : Type uX} {Y : Type uY} {W₁ : Type u₁} {W₂ : Type u₂} {W : Type uW} [Category.{vX, uX} X] [Category.{vY, uY} Y] [Category.{v₁, u₁} W₁] [Category.{v₂, u₂} W₂] [Category.{vW, uW} W] {C : Correspondence X Y W₁} {C' : Correspondence Y X W₂} {E : Correspondence X X W} {e : Enhancement W} {P : W₁} {R : RightAdjointKernelData C C' P} {D : ConvolutionData C C' E} {U : UnitKernelData E} (S : AdjunctionUnitKernelConeData C C' E e P R D U) :
              W

              The selected kernel presenting the conventional cotwist: shift the enhanced unit cone by -1 before transporting it to the ordinary kernel category.

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                The kernel family's shift comparison identifies the transform of cotwistKernel with the pointwise shifted cotwist-cone functor.

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                  The conventional cotwist is a Fourier--Mukai kernel functor, presented by the explicitly named shifted cone kernel. This asserts neither exactness nor invertibility of the cotwist.

                  The transported second map from Φ_P ⋙ Φ_Q to the unshifted cotwist-cone candidate.

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                    The transported connecting map from the unshifted cotwist-cone candidate to the shifted identity functor.

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                      The source-natural unshifted unit triangle 𝟙 X ⟶ Φ_P ⋙ Φ_Q ⟶ cotwistCone ⟶ (𝟙 X)⟦1⟧.

                      Its first map and all three vertices are literal. It is only an objectwise distinguished family, not a distinguished triangle in a functor category.

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                        The conventional cotwist triangle #

                        The inverse rotation of the unshifted unit triangle: cotwist ⟶ 𝟭 X ⟶ Φ_P ⋙ Φ_Q ⟶ cotwist⟦1⟧.

                        Mathlib's inverse rotation owns the minus sign in the first map.

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                          The first projection of the rotated triangle is strictly the pointwise shifted cotwist-cone functor.

                          The third projection of the rotated triangle is strictly the composite adjoint transform.

                          At the natural-transformation level, the second map is strictly the adjunction unit.

                          @[simp]

                          Inverse rotation moves the adjunction unit into the second map.

                          The conventional cotwist-triangle family with codomain restricted to distinguished triangles.

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