Full radical concentration in the primitive factor's direct height #
theorem
MagnitudeConjecture.RightModule.FiniteIndecomposableSkeleton.PrimitiveDirectedBoundaryData.directHeight_radical_concentration
{k A : Type u}
[Field k]
[Ring A]
[Algebra k A]
[FiniteDimensional k A]
[IsNoetherianRing Aᵐᵒᵖ]
[IsAlgClosed k]
{S : FiniteIndecomposableSkeleton k A}
{K : Set (Fin S.n)}
{D : S.PrimitiveMultiplicityInput K}
(B : S.PrimitiveDirectedBoundaryData D)
{X Y : S.SurvivingLabel K}
(hxy : B.directFactorHeight X < B.directFactorHeight Y)
:
((S.factorFiniteTauCategoryData K).radical.ideal.pow (B.directFactorHeight Y - B.directFactorHeight X)).hom
(S.factorObject K X) (S.factorObject K Y) = ⊤ ∧ ((S.factorFiniteTauCategoryData K).radical.ideal.pow (B.directFactorHeight Y - B.directFactorHeight X + 1)).hom
(S.factorObject K X) (S.factorObject K Y) = ⊥
At positive height difference, the full Hom space is concentrated in that radical layer.
theorem
MagnitudeConjecture.RightModule.FiniteIndecomposableSkeleton.PrimitiveDirectedBoundaryData.directHeight_radical_concentration_of_hom
{k A : Type u}
[Field k]
[Ring A]
[Algebra k A]
[FiniteDimensional k A]
[IsNoetherianRing Aᵐᵒᵖ]
[IsAlgClosed k]
{S : FiniteIndecomposableSkeleton k A}
{K : Set (Fin S.n)}
{D : S.PrimitiveMultiplicityInput K}
(B : S.PrimitiveDirectedBoundaryData D)
{X Y : S.SurvivingLabel K}
(hXY : X ≠ Y)
(f : S.factorObject K X ⟶ S.factorObject K Y)
(hf : f ≠ 0)
:
0 < B.directFactorHeight Y - B.directFactorHeight X ∧ ((S.factorFiniteTauCategoryData K).radical.ideal.pow (B.directFactorHeight Y - B.directFactorHeight X)).hom
(S.factorObject K X) (S.factorObject K Y) = ⊤ ∧ ((S.factorFiniteTauCategoryData K).radical.ideal.pow (B.directFactorHeight Y - B.directFactorHeight X + 1)).hom
(S.factorObject K X) (S.factorObject K Y) = ⊥
For distinct labels with a nonzero map, the height difference is positive, the corresponding radical power is the whole Hom group, and the next vanishes.