Exact defects form Serre subcategories #
The coherent-duality equivalence is defined on exact defects. To compare uniseriality there with uniseriality in the ambient finite-functor category, we identify the exact defects by their vanishing on projective or injective modules. This file begins with the two direct vanishing implications.
Finite contravariant functors vanishing on the chosen projective indecomposables.
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Finite covariant functors vanishing on the chosen injective indecomposables.
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A contravariant exact defect vanishes at every projective chosen indecomposable.
A covariant exact defect vanishes at every injective chosen indecomposable.
Exact contravariant defects satisfy projective vanishing.
Exact covariant defects satisfy injective vanishing.
If the cokernel of a restricted contravariant representable map vanishes on projective indecomposables, then the presenting module map is an epimorphism.
If the cokernel of a restricted covariant representable map vanishes on injective indecomposables, then the presenting module map is a monomorphism.
Projective vanishing is sufficient for a finite contravariant functor to admit an exact representable presentation.
Injective vanishing is sufficient for a finite covariant functor to admit an exact representable presentation.
Exact contravariant defects are precisely the finite functors vanishing on projective indecomposables.
Exact covariant defects are precisely the finite functors vanishing on injective indecomposables.
Passing to the exact contravariant-defect subcategory does not change whether an exact defect is uniserial.
Passing to the exact covariant-defect subcategory does not change whether an exact defect is uniserial.
Auslander's coherent anti-equivalence preserves uniseriality for the two defects attached to the same short exact module presentation.