most recent 30 from http://mathoverflow.net 2013-05-20T07:32:57Z http://mathoverflow.net/feeds/user/4226 http://www.creativecommons.org/licenses/by-nc/2.5/rdf http://mathoverflow.net/questions/15658/how-do-i-know-the-derived-category-is-not-abelian/16304#16304 Sunil Rana 2010-02-24T21:33:45Z 2010-02-24T21:33:45Z

<p>Even the homotopy category K(A) is not abelian. given any f in C(A) the 1: cone(f) ---> cone(f) is homotopic to 0 morphism. but homotopy for their kernels doesn't make sense. Well, this is kind of wague, but can be made precise.</p>