Automatic numerical action of the scalar-linear object twist #
The generic scalar-linear twist formulas consume an explicit
LinearEvaluationData.IsEulerCopower witness. Over a field, finite bounded
H⁰ Hom-spaces and the existence of scalar-linear copowers now construct that
witness automatically, so the numerical Seidel--Thomas formula needs no
additional presentation data.
Exactness comes from the generic dg-functor theorem, not from Hom-finiteness or formality; no sphericality or autoequivalence is inferred.
theorem
CategoryTheory.LinearEvaluationData.TwistConeData.twistK₀Of_eq_twistK₀_ofHomFiniteBounded
(k : Type v)
[Field k]
{C : Type u}
[DGCategory C]
[IsPretriangulated C]
[(X Y : C) → (p : ℤ) → Module k ↑((DGCategoryStruct.dgHom X Y).X p)]
[DGLinear k C]
[Triangulated.HomFiniteBounded k (H0 C)]
[∀ (n : ℤ), Functor.Linear k (shiftFunctor (H0 C) n)]
[HasLinearCopowers k C]
{E : C}
{V : LinearEvaluationData k E}
(K : TwistConeData k V)
(X : H0 C)
:
Triangulated.K₀.of (H0 C) (K.twist.h0.obj X) = (Triangulated.SphericalTwist.twistK₀ k (H0 C)
(have this := E;
this))
(Triangulated.K₀.of (H0 C) X)
When all scalar-linear copowers exist, field formality and
HomFiniteBounded automatically identify the evaluation-cone class with the
numerical twist class.
theorem
CategoryTheory.LinearEvaluationData.TwistConeData.twistK₀Map_eq_twistK₀_ofHomFiniteBounded
(k : Type v)
[Field k]
{C : Type u}
[DGCategory C]
[IsPretriangulated C]
[(X Y : C) → (p : ℤ) → Module k ↑((DGCategoryStruct.dgHom X Y).X p)]
[DGLinear k C]
[Triangulated.HomFiniteBounded k (H0 C)]
[∀ (n : ℤ), Functor.Linear k (shiftFunctor (H0 C) n)]
[HasLinearCopowers k C]
{E : C}
{V : LinearEvaluationData k E}
(K : TwistConeData k V)
:
Triangulated.K₀.map K.twist.h0 = Triangulated.SphericalTwist.twistK₀ k (H0 C)
(have this := E;
this)
The induced endomorphism is the numerical twist without a separately supplied Euler copower witness.