most recent 30 from http://mathoverflow.net 2013-05-19T17:09:02Z http://mathoverflow.net/feeds/question/107286 http://www.creativecommons.org/licenses/by-nc/2.5/rdf http://mathoverflow.net/questions/107286/characterization-of-the-sequences-in-the-equivalence-classe-of-the-zero-element-i Arkandias 2012-09-15T20:14:10Z 2012-10-02T10:39:11Z

<p>Hello,</p> <p>I am looking for a characterization of the long exact sequences in the equivalence classe of the zero element (for the Baer sum) in $Ext^n(U,V)$ for $n>1$.</p> <p>If $n=1$, then these are the split short exact sequences.</p> <p>If $n>1$, then the trivial extension $$0 \to V \to V \to 0 \to ... \to 0 \to U \to U \to 0$$ is a representative of the zero class, but how to characterizes the others ?</p> <p>Thanks</p>