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(Co)chain complexes, abelian Categories, (pre)sheaves, (co)homology in various (possibly highly generalized) settings, spectra, derived functors, resolutions, spectral sequences, homotopy categories. Chain complexes in an abelian category form the heart of homological algebra.

8 votes
4 answers
733 views

Tensored Over Abelian Groups?

Suppose I have an category additive category C (i.e. the hom sets are enriched in abelian groups and there are finite direct sums). Suppose further that C has cokernels. Then I can make C tensored ove …
Chris Schommer-Pries's user avatar
5 votes
2 answers
662 views

Terminology: Is there a name for a category with biproducts?

Many people are familiar with the notion of an additive category. This is a category with the following properties: (1) It contains a zero object (an object which is both initial and terminal). Thi …
Chris Schommer-Pries's user avatar
12 votes
2 answers
1k views

Failure of Fin. Presented and Fin. Generated Modules to be Abelian Categories?

Let R be a ring. I'm trying to understand when the categories of finitely presented R-modules and finitely generated R-modules can fail to be abelian categories. Poking around on the internet has le …
Chris Schommer-Pries's user avatar
5 votes
1 answer
269 views

Classifying Algebra Extensions over a fixed extension?

There are lots of "Ext groups" in homological algebra which measure extensions of various things. I'm sure there must be a homological algebra machine for computing the following, and I'm hoping that …
Chris Schommer-Pries's user avatar
34 votes
2 answers
5k views

Example Wanted: When Does Čech Cohomology Fail to be the same as Derived Functor Cohomology?

I want to know exactly how derived functor cohomology and Cech cohomology can fail to be the same. I started worrying about this from Dinakar Muthiah's answer to an MO question, and Brian Conrad's com …
Chris Schommer-Pries's user avatar
25 votes
4 answers
3k views

A Peculiar Model Structure on Simplicial Sets?

I'm wondering if there is a Quillen model structure on the category of simplicial sets which generalizes the usual model structure, but where every simplicial set is fibrant? I want to use this to do …
Chris Schommer-Pries's user avatar
27 votes
13 answers
4k views

Homological algebra for commutative monoids?

Homological algebra for abelian groups is a standard tool in many fields of mathematics. How much carries over to the setting of commutative monoids (with unit)? It seems like there is a notion of sho …
Chris Schommer-Pries's user avatar