The modules V_X̃ over finite subcategories of L #
Lemma 4.8 and the first step of Lemma 4.13 (scalar-normalization.tex). L is the graded covering category on the lifted
projective vertices (grading0). For a lifted object X̃ = (X, h) and a finite
set T of lifted projective vertices, V_X̃ restricted to T is a module over
the covering algebra cov T (VM): its value at z = (p, g) is the degree
g⁻¹h part of C(P_p, X), and L acts by composition. When T contains the
support of V_X̃ it is finite-dimensional and indecomposable: "Height gives
End(V_X̃) = k, so the modules are indecomposable" (VM_isFiniteIndecomposable,
via Lemma 4.8).
Restricting a grading to a subfamily #
The restriction of a grading to a subfamily.
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The restriction of height data to a subfamily with distinct labels.
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The grading of L: the deck grading on the projective labels.
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The finite set T as objects of L.
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The covering algebra of T.
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V_X̃ on T: at z = (p, g) the degree g⁻¹h part of C(P_p, X).
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Elements of the covering algebra as matrices.
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The underlying morphisms.
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The module V_X̃|_T over the covering algebra.
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The identity from the native k-structure.
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Matrix units and components #
The matrix unit of a morphism u : q' → q of L between objects of T.
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A component concentrated at one object of T.
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Maps V_X̃ → V_Ỹ that scale the action of matrix units by d.
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Natural families from module maps #
T contains the support of V_X̃.
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A family of maps C̃(P_z, X̃) → C̃(P_z, Ỹ) scaled by d along L.
- φ (z : D.PV × G) : (F ↑z.1 ⟶ F X.1) →ₗ[k] F ↑z.1 ⟶ F Y.1
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An unscaled family is natural.
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The components of a map V_X̃|_T → V_Ỹ|_T, extended by zero.
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A scaled module map gives a scaled family.
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Indecomposability #
A module map as a k-linear map for the native structures.
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Endomorphisms of V_X̃ are scalars ("Height gives End(V_X̃) = k").
V_X̃|_T is finite-dimensional and indecomposable.