1. P. M. Cohn,Universal Algebra Harper and Row, New York, 1965.
2. P. Freyd,Abelian Categories: An Introduction to the Theory of Functors Harper and Row, New York, 1964.
3. Y. Give'on, Dissertation, University of Michigan, 1966. (Appeared also as Technical Report No. 03105-43-T, O.R.A., The University of Michigan, 1966.)
4. Y. Give'on, “An Introduction to the Algebraic Theory of Transition Systems”, notes on material presented in a lecture series at Case Institute of Technology, February 1966 (to be published).
5. S. MacLane,Homology Academic Press, New York, 1963.