Radical morphisms in a finite deck-orbit category #
For locally finite objects with local endomorphism rings and a deck action free on isomorphism classes, a finite-support shift-orbit morphism is radical exactly when each of its homogeneous components is radical upstairs. This is the pointwise input for push-down of the projective radical boundary.
A local endomorphism ring makes its object nonzero.
A split monomorphism into an object with local endomorphism ring is an isomorphism as soon as its source is nonzero. Unlike the biproduct version, this uses only the local-ring idempotent dichotomy.
A homogeneous orbit morphism is the degree-zero inclusion of its underlying map followed by the canonical isomorphism from the shifted target back to the target.
Split-monicity of a homogeneous orbit morphism is equivalent to split-monicity of its upstairs component.
With local endomorphism rings on the upstairs source and the orbit source, a homogeneous orbit morphism is radical exactly when its component is radical upstairs.
Triviality of the shift stabilizer makes the degree of an isomorphism between two translates unique.
Under localness and a trivial target shift stabilizer, a shift-orbit morphism is radical exactly when all homogeneous components are radical.
The diagonal inclusion from the push-down of rad(X,-) into the
push-down of Hom(X,-), followed by the canonical orbit-representable
comparison.
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Pointwise, the preceding comparison simply forgets each component's radical-membership proof.
Before choosing orbit representatives, push-down of the radical representable maps canonically to the radical of the orbit representable.
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The raw orbit radical comparison is an isomorphism: its inverse regroups the finitely many homogeneous radical components.
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The raw radical comparison is the restriction of the canonical projective-representable push-down comparison.
Freeness of the deck action on isomorphism classes gives a trivial stabilizer for every object under the associated additive shift.
The shift-orbit endomorphism ring of every upstairs object is local. It is transported from the corresponding deck-orbit-skeleton vertex.
Deck-specialized componentwise criterion for categorical radical morphisms in the shift-orbit category.
Before choosing orbit representatives, Gabriel push-down sends the radical of an upstairs projective representable to the radical of the corresponding shift-orbit representable.
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The deck-specialized raw radical comparison is compatible with the projective-representable comparison.
Radicality agrees in the chosen orbit skeleton and in the ambient shift-orbit category.
At chosen representatives, the ambient and induced-category radical Hom spaces are canonically linearly equivalent.
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Restricting the radical representable at a chosen representative gives the literal radical representable on the deck-orbit skeleton.
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The chosen-representative radical comparison is the restriction of the corresponding representable comparison.
Skeletal Gabriel push-down sends the radical of the projective
representable at X to the radical of the projective representable at the
strict orbit of X.
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The skeletal radical comparison and projective-representable comparison identify the pushed radical inclusion with the literal downstairs radical inclusion.
Bundled linear-module form of skeletal push-down preserving the radical of a projective representable.
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The finite downstairs radical projective associated to the strict orbit
of X.
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Finite-dimensional skeletal push-down preserves the radical of a finite projective representable.
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Finite-dimensional push-down carries the literal radical inclusion of an upstairs projective representable to the literal radical inclusion of the corresponding downstairs projective representable.
Finite-dimensional skeletal push-down sends the radical inclusion of a projective representable to a right almost-split morphism.
Projective boundary adjacency: every indecomposable with an irreducible map to the push-down of an upstairs projective representable is itself the push-down of an upstairs indecomposable.