1. Exact categories;Barr,1971
2. Homology and standard constructions;Barr,1969
3. A survey of semi-abelian categories;Borceux,2004
4. Mal'cev, Protomodular, Homological and Semi-Abelian Categories;Borceux,2004
5. Normalization equivalence, kernel equivalence and affine categories;Bourn,1991