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Extending the work of Fröhlich, Lue and Furtado-Coelho, we consider the theory of Baer invariants in the context of semi-abelian categories. Several exact sequences, relative to a subfunctor of the identity functor, are obtained. We consider a notion of commutator which, in the case of abelianization, corresponds to Smith's. The resulting notion of centrality fits into Janelidze and Kelly's theory of central extensions. Finally we propose a notion of nilpotency, relative to a Birkhoff subcategory of a semi-abelian category.
@article{TAC_2004_12_a0, author = {T. Everaert and T. Van der Linden}, title = {Baer invariants in semi-abelian categories {I:} {General} theory}, journal = {Theory and applications of categories}, pages = {1--33}, publisher = {mathdoc}, volume = {12}, year = {2004}, language = {en}, url = {http://geodesic.mathdoc.fr/item/TAC_2004_12_a0/} }
T. Everaert; T. Van der Linden. Baer invariants in semi-abelian categories I: General theory. Theory and applications of categories, Tome 12 (2004), pp. 1-33. http://geodesic.mathdoc.fr/item/TAC_2004_12_a0/