The converse of Corollary 4.15: A ≅ A₀ implies that A is standard #
scalar-normalization.tex: "Conversely an isomorphism A ≅ A₀ gives an equivalence
F : ind(mod A) → C, possibly permuting labels. Since C is generated in degree one with
homogeneous relations, gr_J C = C. Thus gr F is a graded automorphism of C with the same
permutation. Applying (gr F)⁻¹ after F gives the required object-preserving equivalence."
An isomorphism ψ : A ≅ A₀ makes the evaluated modules M_x of C = k(Γ_A) into
indecomposable A-modules, which identifies C with ind(mod A) up to a permutation σ of the
labels (Φ). Under Φ the radical powers of ind(mod A) are the morphisms of degree at least
m of C (gr_J C = C, MeshRadical). Deviation: instead of correcting F by (gr F)⁻¹, the
degree-one parts of the arrow representatives are taken as lifts; their mesh errors are of degree
two and lie in J³, so they vanish, and the filtered normal form (Lifts.functor) gives the
object-preserving equivalence (isStandard_of_algEquiv).
The algebra A₀ of A.
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Bᵐᵒᵖ ≅ Alg F₀.
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The evaluation C → mod A₀.
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The evaluation C → mod B through ψ.
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The k-action on an evaluated A-module is the natural one.
The evaluated modules are finite-dimensional indecomposable A-modules.
The comparison with a skeleton #
The comparison C(x, y) → ind(mod A)(σ x, σ y).
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Radical powers are degrees #
Under Φ, the radical powers are the morphisms of degree at least m.
The relabelling of ind(mod A) #
The label of the evaluated module of x.
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M_x ≅ X_{σ x}.
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Degree-one lifts and standardness #
The relabelling as an equivalence.
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Transport along the relabelling.
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The arrow representatives read in C.
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The degree-one lifts.
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The mesh error of the degree-one lifts, read in C: homogeneous of degree two.
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The mesh errors of the degree-one lifts vanish.
The converse of Corollary 4.15 (cor:graded-standard-form): if A ≅ A₀, then A is
standard.
The converse of Corollary 4.15 (cor:graded-standard-form): if A ≅ A₀, then A is
standard.