Comparing presented dg and Fourier--Mukai twists #
Suppose a strict dg adjunction is presented on ordinary categories by a pair of Fourier--Mukai transforms. A chosen dg cone on its counit and an independently chosen enhanced Fourier--Mukai cone then give two pointwise distinguished counit triangles with the same first two vertices and the same first map.
Mathlib's isoTriangleOfIso₁₂ supplies a noncanonical isomorphism between
the two triangles at each target object. Its third component compares the
ordinary transport of the actual dg twist with the Fourier--Mukai twist.
The unconditional completion is chosen separately at each object and
therefore supplies no naturality. A separate PresentedCounitComparisonData
interface records a genuinely supplied natural twist isomorphism and its two
remaining triangle squares; from that input the file constructs the natural
counit-triangle isomorphism. It does not construct this input or prove
independence of either cone choice. Under an explicit equivalence hypothesis
on the dg twist at H⁰, the comparison packages the selected kernel as a
KernelAutoequivalence; it does not prove that hypothesis or sphericality. A
further ShiftCompatibility
refinement can select a Fourier--Mukai CommShift structure compatible with
the comparison; exactness then transfers through Mathlib's existing
Functor.isTriangulated_of_iso theorem.
At each target object, the presented dg counit triangle is noncanonically isomorphic to the independently chosen Fourier--Mukai counit triangle.
The isomorphism is the identity on the adjunction-composite and identity
vertices. Its third component is the choice made by triangulated-category
completion and is not asserted to be natural in Z.
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The first component of the counit-triangle comparison is the identity.
The second component of the counit-triangle comparison is the identity.
The resulting noncanonical objectwise comparison between the transported actual dg twist and the Fourier--Mukai twist.
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Supplied natural comparison data #
The genuinely additional data required to supply a separate natural counit-cone comparison of the same triangle families considered objectwise above.
This is a semantic abbreviation of the generic comparison between two first-map normalizations. It stores a natural isomorphism of the twist functors and compatibility with the two remaining triangle maps.
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Supply a natural comparison of the transported dg and Fourier--Mukai twists, together with exactly the two triangle-map squares not fixed by the common adjunction counit.
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- CategoryTheory.Triangulated.FourierMukai.CounitKernelConeData.PresentedCounitComparisonData.ofTwistIso adj H K S hE iso second third = { thirdIso := iso, second := second, third := third }
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The supplied comparison data determine a natural isomorphism between the presented dg and Fourier--Mukai counit-triangle families.
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The natural counit-triangle comparison is the identity on the adjunction composite vertex.
The natural counit-triangle comparison is the identity on the identity vertex.
The third component of the natural counit-triangle comparison is the supplied twist isomorphism.
The induced natural isomorphism from the transported actual dg twist to the Fourier--Mukai twist.
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The projected twist isomorphism is the third-vertex isomorphism supplied by the endpoint-strict comparison data.
The transported actual dg twist is a kernel functor once a natural comparison with the selected Fourier--Mukai twist has been supplied.
An explicit equivalence hypothesis on H⁰ of the dg twist transfers to the
selected Fourier--Mukai twist through the supplied natural comparison.
The selected twist kernel, packaged as a kernel autoequivalence under the
explicit equivalence hypothesis on H⁰ of the dg twist.
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Compatibility with selected shift structures #
The twist-specific specialization of the shared comparison-shift package.
The source is fixed to the canonical shift structure on the transported H⁰
dg twist; the target structure remains independently selected by the
realization.
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The selected transported H⁰ shift structure on the dg twist.
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The selected shift structure on the Fourier--Mukai twist.
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The twist comparison respects its selected source and target shift structures.
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- ⋯ = ⋯
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The Fourier--Mukai twist is triangulated relative to the selected target shift structure when the supplied comparison respects shifts.
The kernel autoequivalence of the selected Fourier--Mukai twist is an exact equivalence relative to the selected target shift package.