Classification problems in K-categories
Closedness properties of internal relations. IV: Expressing additivity of a category via subtractivity.
Closure operators in exact completions.
Cohomology without projectives
Comparing coequalizer and exact completions.
Construction de théories d'exactitude
Derived functors of and abelian ab3*- and Ab4*-categories with enough injectives
Diagram lemmas in semi-exact -categories
Dualization in algebraic K-theory and the invariant e¹ of quadratic forms over schemes
In the classical Witt theory over a field F, the study of quadratic forms begins with two simple invariants: the dimension of a form modulo 2, called the dimension index and denoted e⁰: W(F) → ℤ/2, and the discriminant e¹ with values in k₁(F) = F*/F*², which behaves well on the fundamental ideal I(F)= ker(e⁰). Here a more sophisticated situation is considered, of quadratic forms over a scheme and, more generally, over an exact category with duality. Our purposes are: ...
Essential localizations and infinitary exact completion.
Étude élémentaire des catégories
Exact completion and representations in abelian categories.
Extension categories and their homotopy
Extensions of covariantly finite subcategories revisited
Extriangulated categories were introduced by Nakaoka and Palu by extracting the similarities between exact categories and triangulated categories. A notion of homotopy cartesian square in an extriangulated category is defined in this article. We prove that in an extriangulated category with enough projective objects, the extension subcategory of two covariantly finite subcategories is covariantly finite. As an application, we give a simultaneous generalization of a result of X. W. Chen (2009) and...
Free algebras and automata realizations in the language of categories
Functors on locally finitely presented additive categories
Gorenstein dimension of abelian categories arising from cluster tilting subcategories
Let be a triangulated category and be a cluster tilting subcategory of . Koenig and Zhu showed that the quotient category is Gorenstein of Gorenstein dimension at most one. But this is not always true when becomes an exact category. The notion of an extriangulated category was introduced by Nakaoka and Palu as a simultaneous generalization of exact categories and triangulated categories. Now let be an extriangulated category with enough projectives and enough injectives, and a cluster...
Hall algebras of two equivalent extriangulated categories
For any positive integer , let be a linearly oriented quiver of type with vertices. It is well-known that the quotient of an exact category by projective-injectives is an extriangulated category. We show that there exists an extriangulated equivalence between the extriangulated categories and , where and are the two extriangulated categories corresponding to the representation category of and the morphism category of projective representations of , respectively. As a by-product,...
Higher-dimensional Auslander-Reiten sequences
Zhou and Zhu have shown that if is an -angulated category and is a cluster tilting subcategory of , then the quotient category is an -abelian category. We show that if has Auslander-Reiten -angles, then has Auslander-Reiten -exact sequences.
Homology of -fold groupoids.