1. Arbib, M.A.; Manes, E.G.: Arrows, Structures and Functors: The Categorical Imperative, Academic Press, New York, 1975
2. Herrlich, H.; Strecker G.: Category Theory, Allyn and Bacon, Rockleigh 1973
3. Herman, G.T.; Rozenberg, G.: Developmental Systems and Languages, North Holland, Amsterdam, 1975