1. H. Cartan, S. Eilenberg, Homological Algebra. Princeton University Press, Princeton, 1956.
2. T. Datuashvili, On the global homological dimension of extensions of rings. Bulletin Acad.Sci.Georgian SSR, 100, No.2, 1980, 301–304 (Russian)
3. T. Datuashvili, On the homological dimension of extensions of abelian categories and rings. Bulletin Acad.Sci.Georgian SSR, 101, No.1, 1981, 37–40 (Russian).
4. T. Datuashvili, On the homological dimension of extensions of abelian categories. Proc. Math. Inst. Tbilisi, Acad.Sci.Georgian SSR, vol. LXX, 1982, 24–41 (Russian).
5. R. Fossum, P. Griffith and I. Reiten, Trivial extensions of abelian categories and applications to rings: an expository account, mimeographed notes. University of Illinois, Urbana, 1971.