A topological group $X$ is called $duoseparable$ if there exists a countable set $S\subseteq X$ such that $SUS=X$ for any neighborhood $U\subseteq of the unit. We construct functor $F$ assigning to each (abelian) duoseparable (abelain-by-cyclic) $FX$, containing an isomorphic copy $X$. In fact, defined on category unital topologized magmas. Also we prove $\sigma$-compact locally compact abelian...

The category of representations of a finite quiver in the category of sheaves of modules on a ringed space is abelian. We show that this category has enough injectives by constructing an explicit injective resolution. From this resolution we deduce a long exact sequence relating the Ext groups in these two categories. We also show that under some hypotheses, the Ext groups are isomorphic to cer...

We show that there are no gaps in the lengths of the indecomposable objects in an abelian k-linear category over a field k provided all simples are absolutely simple. To derive this natural result we prove that any distributive minimal representation-infinite k-category is isomorphic to the linearization of the associated ray category which is shown to have an interval-finite universal cover wi...

When the exact completion of a category with weak finite limits is a Mal’cev category, it is possible to combine the universal property of the exact completion and the universal property of the coequalizer completion. We use this fact to explain Freyd’s representation theorems in abelian and Frobenius categories. MSC 2000 : 18A35, 18B15, 18E10, 18G05.

1 Brown Representability First we introduce a portly abelian category A(S) for any preadditive category S. This will be a certain full subcategory of the category of all contravariant additive functors S −→ Ab. Modulo the fact that S is not assumed to be small, this is precisely what we call a right module over a ringoid in our Rings With Several Objects (RSO) notes. For background on portly ab...

We review Quillen’s concept of a model category as the proper setting for defining derived functors in non-abelian settings, explain how one can transport a model structure from one category to another by mean of adjoint functors (under suitable assumptions), and define such structures for categories of cosimplicial coalgebras.

We use twisted Fourier-Mukai transforms to study the relation between an abelian fibration on a holomorphic symplectic manifold and its dual fibration. Our reasoning leads to an equivalence between the derived category of coherent sheaves on one space and the derived category of twisted sheaves on the other space.

For any free partially commutative monoid M(E, I), we compute the global dimension of the category of M(E, I)-objects in an Abelian category with exact coproducts. As a corollary, we generalize Hilbert’s Syzygy Theorem to polynomial rings in partially commuting variables.

We define an unstable equivariant motivic homotopy category for an algebraic group over a Noetherian base scheme. We show that equivariant algebraic K-theory is representable in the resulting homotopy category. Additionally, we establish homotopical purity and blow-up theorems for finite abelian groups.

Let M be a non–compact, connected manifold of dimension ≥ 1. Let D(sheaves/M) be the unbounded derived category of chain complexes of sheaves of abelian groups on M . We prove that D(sheaves/M) is not a compactly generated triangulated category, but is well generated. 2000 Mathematics Subject Classification: 18E30 55P99 55U35