Local normalization on the standard-form universal cover #
Square-freeness makes the indecomposable labels in a displayed mesh middle term pairwise distinct. If every realized sink is minimal right almost split, then every assigned arrow is irreducible. The paired arrows in one lifted mesh therefore assemble into a minimal left almost-split map: after factoring its components through the chosen left almost-split source, the comparison endomorphism has invertible diagonal entries and hence is an automorphism by the finite Krull--Schmidt matrix theorem.
Twisting the chosen right sink by the inverse comparison makes the lifted mesh relation hold literally while preserving minimal right almost-splitness.
Precomposition by an isomorphism preserves right minimality.
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The official middle labels of a standard-form right mesh are pairwise distinct.
A component cut out by a split inclusion from a minimal right almost-split morphism between selected indecomposables is irreducible.
Under the global sink invariant, every universal-cover arrow representative is irreducible.
The representatives on the polarized partner arrows assemble into a minimal left almost-split map. More precisely, they differ from the chosen right-mesh source by an automorphism of the displayed middle term.
The canonical comparison automorphism between the chosen mesh source and the source assembled from a sink-compatible universal assignment.
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The comparison automorphism realizes the assembled source exactly.
The source assembled from a sink-compatible universal assignment is left almost split.
The source assembled from a sink-compatible universal assignment is left minimal.
Twist the chosen downstairs right sink so that its source is the source assembled from the current universal arrow assignment.
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The locally normalized source and sink have zero composite.
The locally normalized source and sink have zero composite.
The locally normalized sink remains right almost split.
The locally normalized sink remains right minimal.
At one height, use the normalized sink at nonprojective vertices and leave the current realized sink unchanged at projective vertices.
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Simultaneously normalize every nonprojective lifted mesh at one height, while retaining projective sinks.
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Height normalization preserves the global minimal right almost-split sink invariant.
Replacing sinks at height m does not change the source of a mesh whose
endpoint has height m: every paired arrow used by that source starts one
height lower.
Every nonprojective mesh at the selected height satisfies its literal zero relation after simultaneous normalization.
An arrow assignment together with the global minimal right almost-split sink invariant needed by the positive-height induction.
- arrowMap : S.StandardFormUniversalArrowAssignment x₀
- sinkCondition : S.StandardFormUniversalSinkCondition x₀ fun {W Z : MeshCategory.RightMeshData.UniversalCover.Vertex S.standardFormRightMeshData x₀} => self.arrowMap
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The occurrence-component assignment is the initial state of the positive-height induction.
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Normalize all sinks at one height while retaining the global sink invariant.
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Stage n of the positive induction has normalized precisely the positive
heights 1, ..., n.
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The positive limiting assignment. An arrow whose source has positive
height n takes its representative from stage n; arrows of nonpositive
source height retain their initial representatives.
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At a source of natural-number height n, the positive limiting
assignment agrees with stage n.
The successor positive stage changes only arrows whose source has the newly processed height.
At a vertex of natural-number height n, the limiting realized sink is
already the sink of stage n.
For a mesh ending at height n + 1, its source in the limiting
assignment is already its source at stage n + 1. Its paired arrows start
at height n, so the successor stage leaves them unchanged.
Every mesh whose endpoint has positive natural-number height satisfies its literal zero relation in the positive limiting assignment.
At a nonpositive source height, the positive induction leaves the realized sink equal to its initial value.
Passing to the pointwise positive limit preserves the global minimal right almost-split sink invariant.
Every nonprojective mesh at positive height satisfies its literal zero relation in the positive limiting assignment.