Riedtmann covering theorem for the normalized universal realization #
This file implements the radical-layer argument of Riedtmann, Proposition 2.3, for the normalized standard-form universal mesh functor. The right almost-split half first approximates every fixed-target morphism by lifted mesh paths modulo successive powers of the categorical radical.
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The scalar residue remainder of an endomorphism of a chosen indecomposable is radical, hence is not split epic.
The scalar residue remainder of an indecomposable endomorphism is also not split monic.
A morphism between two differently labelled chosen indecomposables is not split epic.
A morphism between two differently labelled chosen indecomposables is not split monic.
A universal-cover vertex as an object of its raw mesh category.
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The skeletal realization sends the mesh object represented by W to
its base label.
The possible degree-zero contribution in a fixed-source target fibre. It is supported at the source vertex itself when its base label is the fixed downstairs target, and is zero otherwise.
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The possible degree-zero contribution in a fixed-target source fibre. It is supported at the target vertex itself when its base label is the fixed downstairs source, and is zero otherwise.
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The raw mesh-category morphism represented by one displayed arrow into
the lifted sink at W.
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The skeletal realization of the displayed raw mesh arrow is its chosen normalized irreducible module map.
The displayed middle arrow with its literal underlying module-Hom type. This wrapper keeps object-definition transports out of additive formulas.
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The image of an arbitrary incoming arrow is its normalized irreducible representative. This star-indexed form avoids transports through the chosen finite enumeration of the middle term.
An arbitrary incoming arrow after realization, with its literal underlying module-Hom type.
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The image of an arbitrary categorical outgoing arrow is its normalized irreducible representative.
An arbitrary outgoing categorical arrow after realization, with its literal underlying module-Hom type.
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A dependent arrow assignment applied after transporting the target of a reversed quiver arrow is transported by the corresponding object equality.
Transport the distinguished source vertex of an outgoing costar.
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Realization of an outgoing arrow commutes with transport of its source vertex.
Literal right-mesh occurrences have the official finite-tau arrow multiplicity, including at the projective boundary.
The occurrences of one target in the chosen minimal left-almost-split middle term are equinumerous with the reversed standard-form arrows that represent maps from the fixed source to that target.
Match the chosen left-almost-split summand occurrences at source with
the outgoing reversed standard-form arrows, target by target.
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Square-freeness of the standard-form quiver forces the chosen minimal left-almost-split middle decomposition to contain no repeated label.
Regroup the indices of the chosen minimal left-almost-split middle term by their target labels.
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The chosen left-almost-split middle indices are the categorical outgoing costar of the corresponding base standard-form vertex.
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Lift the left-almost-split middle indices uniquely to the outgoing costar of a selected universal-cover vertex.
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Projecting the lifted outgoing arrow attached to a left-middle index recovers its base costar arrow.
The base label of the lifted outgoing target is the label of its chosen left-almost-split summand.
Reassemble all realized outgoing arrows at W into the chosen minimal
left-almost-split middle term at its base label.
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Every chosen-summand component of the reassembled outgoing source is irreducible.
The source assembled from every outgoing universal-cover arrow differs from the chosen minimal left-almost-split map by an automorphism of its middle term. This includes injective source vertices.
The comparison automorphism between the chosen left-almost-split source and the outgoing source assembled from the normalized realization.
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The chosen left-almost-split map followed by the comparison automorphism is the reassembled outgoing source.
The outgoing source assembled from the normalized universal realization is left almost split at every vertex, including injective vertices.
The outgoing source assembled from the normalized universal realization is left minimal at every vertex.
At a noninjective lifted vertex, the source assembled from all outgoing normalized arrows is monic. Under the comparison automorphism it is the chosen left almost-split monomorphism at the underlying indecomposable.
At a noninjective lifted vertex, the normalized outgoing arrows jointly detect morphisms into that vertex.
Expanding the chosen left-middle biproduct writes a factor through the reassembled outgoing source as the sum of its lifted-arrow components.
Remove the scalar residue of an endomorphism and factor the radical remainder through all normalized outgoing arrows.
A morphism to a differently labelled indecomposable factors through all normalized outgoing arrows at its source.
The fixed-source Riedtmann one-step decomposition, with the scalar identity term already bundled as a target-fibre contribution.
Every outgoing arrow of the normalized universal realization belongs to the categorical radical ideal.
Riedtmann's fixed-source approximation: modulo the n-th radical
power, every module morphism is the image of a finite target-fibre sum of
raw mesh morphisms.
Nilpotence terminates the fixed-source radical approximation, giving exact surjectivity of the target-fibre map at every represented source.
Every fixed-source target-fibre family is a possible scalar at the source vertex plus families precomposed with the arrows leaving that vertex. This is the direct-sum form of decomposition by the first arrow.
The downstairs nonprojective endpoint whose translate is a selected noninjective standard-form label.
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The recovered downstairs mesh endpoint translates to the base label of the selected noninjective lifted vertex.
Reverse the formal mesh edge at a noninjective lifted vertex. The result is the unique lifted nonprojective mesh endpoint whose translate is the original vertex.
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Translating the endpoint obtained by reversing the formal mesh edge recovers the original noninjective lifted vertex.
The raw mesh morphism represented by the polarized partner of an arbitrary incoming arrow at a nonprojective lifted vertex.
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A polarized partner of an arbitrary incoming arrow after realization, with its literal underlying module-Hom type.
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The ordinary mesh relation remains zero after applying it coefficientwise to an entire fixed-target source fibre.
The ordinary mesh relation remains zero after applying it coefficientwise to an entire fixed-source target fibre.
Every incoming arrow of the universal mesh has radical image, without choosing a displayed middle-term index.
Every fixed-target source-fibre family is a possible scalar at the target vertex plus families postcomposed with the arrows entering that vertex. This is the direct-sum form of decomposition by the final arrow.
Every displayed normalized arrow lies in the categorical radical ideal of the representation-finite module category.
At a nonprojective lifted vertex, the normalized mesh source is a weak kernel of the normalized mesh sink. This is the local exactness statement used to peel a relation one mesh layer farther from its endpoint.
At a nonprojective lifted vertex, the normalized mesh sink is a weak cokernel of the normalized mesh source. This is the target-side local exactness statement used to peel a relation one mesh layer farther from its source.
Expanding through the displayed middle biproduct writes a factor through the normalized realized sink as the finite sum of its arrow components.
Assemble the displayed incoming coefficients into the chosen middle term
of the almost-split sink at W.
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A component of the assembled incoming middle map is its displayed coefficient.
A component of the assembled incoming middle map is its displayed coefficient.
Composing the assembled middle map with the normalized sink is the sum of its displayed incoming-arrow composites.
Assemble maps out of the displayed middle summands into a map from the chosen right-mesh middle term.
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Restricting the assembled outgoing middle map to a displayed summand recovers its coefficient.
Restricting the assembled outgoing middle map to a displayed summand recovers its coefficient.
Composing the normalized mesh source with an assembled outgoing middle map is the sum of the polarized-arrow composites.
At a nonprojective lifted endpoint, every relation among the normalized polarized arrows leaving its translate is generated by the arrows entering the endpoint.
Nonprojective outgoing exactness in the star coordinates at the mesh endpoint: a relation among polarized partners factors through the incoming arrows.
Polarization identifies the incoming star of a nonprojective mesh endpoint with the outgoing costar of its translated source.
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The costar arrow obtained by polarization realizes the same normalized map as the corresponding paired incoming arrow.
A vanishing family after all arrows leaving a translated mesh source is obtained by postcomposing the arrows entering the mesh endpoint.
For a noninjective lifted source, its outgoing costar is parametrized by the incoming star of the canonical mesh endpoint whose translate is that source.
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The incoming star arrow associated with an outgoing costar at a noninjective source.
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The incoming arrow associated with an outgoing costar at a noninjective source, with its source definitionally equal to the costar endpoint.
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At a noninjective lifted source, a vanishing outgoing costar family is obtained by postcomposing the incoming arrows at its canonical mesh endpoint.
The mesh relation at the canonical endpoint of a noninjective source, transported to that literal source vertex, vanishes coefficientwise in the target fibre.
Assemble maps from the chosen minimal left-almost-split summands into a map out of its middle term.
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A displayed summand of the assembled left-middle map is its prescribed coefficient.
A displayed summand of the assembled left-middle map is its prescribed coefficient.
Composing the realized outgoing source with an assembled left-middle map is the corresponding finite costar sum.
At an injective source, a relation among the chosen outgoing summands has every coefficient zero.
At an injective lifted source, a vanishing outgoing costar sum has all coefficients zero.
A scalar identity cannot cancel a sum through the normalized outgoing costar arrows.
At a projective lifted endpoint, a vanishing incoming-arrow sum has all displayed coefficients zero.
Projective incoming exactness in the star coordinates produced directly by raw final-arrow decomposition.
At a nonprojective lifted endpoint, a vanishing incoming-arrow sum is the image of the paired mesh-source family.
Nonprojective incoming exactness in the star coordinates produced directly by raw final-arrow decomposition.
A scalar identity cannot cancel a sum through the normalized incoming irreducible arrows.
Star-indexed scalar separation, in the coordinates produced directly by the raw final-arrow decomposition.
One radical-layer step for an endomorphism: remove its scalar residue, then factor the radical remainder through the lifted right almost-split sink.
One radical-layer step between differently labelled indecomposables: the morphism itself factors through the lifted right almost-split sink.
The Riedtmann one-step decomposition, already bundling the scalar identity term as a source-fibre contribution of the mesh functor.
Riedtmann's fixed-target approximation: modulo the n-th radical
power, every module morphism is the image of a finite source-fibre sum of
raw mesh morphisms.
Nilpotence terminates the radical-layer approximation, giving exact surjectivity of the fixed-target source-fibre map at every represented universal-cover vertex.
One exact Riedtmann peeling step in a fixed-target source fibre. A family in the kernel is a sum through the arrows entering the target, and the coefficient family can be chosen in the kernel at every preceding target. In the nonprojective case this is achieved by lifting the common mesh-source factor and subtracting the resulting mesh relation.
One exact Riedtmann peeling step in a fixed-source target fibre. A kernel family is a sum through the arrows leaving its source, with every coefficient family again in the kernel.
Componentwise path-length tail membership for a fixed-target source-fibre family.
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Postcomposition by one displayed incoming arrow raises the componentwise path-length tail by one.
Componentwise path-length tails are separated on a fixed-target source fibre.
Iterated kernel peeling places a fixed-target kernel family in every prescribed path-length tail.
The fixed-target source-fibre map of the normalized universal realization has trivial kernel.
Fixed-target source-fibre injectivity for a displayed universal-cover mesh object.
Every raw mesh-category object is literally represented by its underlying universal-cover vertex, so the fixed-target surjectivity holds for an arbitrary target object.
The fixed-target source-fibre map is injective for an arbitrary raw mesh-category target.
The normalized universal realization satisfies the fixed-target half of the linear covering condition.
Every raw mesh-category source is literally represented by its underlying universal-cover vertex, so fixed-source target-fibre surjectivity holds for an arbitrary source object.
Componentwise path-length tail membership for a fixed-source target-fibre family.
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Precomposition by one displayed outgoing arrow raises the componentwise path-length tail by one.
Componentwise path-length tails are separated on a fixed-source target fibre.
Iterated kernel peeling places a fixed-source kernel family in every prescribed path-length tail.
The fixed-source target-fibre map of the normalized universal realization has trivial kernel.
Fixed-source target-fibre injectivity for a displayed universal-cover mesh object.
The fixed-source target-fibre map is injective for an arbitrary raw mesh-category source.
The normalized universal realization satisfies the fixed-source half of the linear covering condition.
The normalized standard-form realization of the universal mesh category is a linear covering functor.