1. Exact Categories and Categories of Sheaves;Barr,1971
2. Mal'cev, Protomodular, Homological and Semi-Abelian Categories;Borceux,2004
3. Congruence distributivity in Goursat and Mal'tsev categories;Bourn;Appl. Categ. Struct.,2005
4. Categorical aspects of modularity;Bourn,2004
5. Normal sections and direct product decompositions;Bourn;Commun. Algebra,2004