[4] MacLane S.: Categorical Algebra. New York 1963.
[5] Johnson A. A.: Dissertation. Case Institute of Technology 1959.
[6] Eilenberg S., MacLanc S.:
General theory of natural equivalences. Trans. Amer. Math. Soc. 58 (1945), 231-294.
MR 0013131
[7] MacLanc S.:
Homology. Berlin-Gőttingen-Heidelberg 1963.
MR 0156879