1. Amgott, S.M.,Separable categories. J. Pure Appl. Algebra 40 (1986), 1–14.
2. Lecture Notes in Math.;P. Deligne,1982
3. Hoehnke, H.-J.,Spatial matrix systems and their theories.A contribution to bilinear algebra. Proceedings of the 2. Symposium on N-ary Structures, Varna 1983 (V. Topencharov ed.), Sofia 1985.
4. Mac Lane, S.,Kategorien.Begriffssprache und mathematische Theorie. Springer-Verlag, Berlin 1972.
5. Mitchell, B.,Rings with several objects. Advances in Math. 8 (1972), 1–161.