Universal central extensions in semi-abelian categories

Abstract

Basing ourselves on Janelidze and Kelly's general notion of central extension, we study universal central extensions in the context of semi-abelian categories. We consider a new fundamental condition on composition of central extensions and give examples of categories which do, or do not, satisfy this condition.

12 pages, compact revised and published version of the paper arXiv:0908.3762

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