1. Samson Abramsky, Simon J. Gay, and Rajagopal Nagarajan. Interaction categories and the foundation of typed concurrent programming. In M.Broy, editor, Deductive Program Design: Proceedings of the 1994 Marktoberdorf Summer School, NATO ASI Series F: Computer and System Sciences. Springer Verlag, 1994.
2. Micheal Barr and Charles Wells. Category Theory for Computing Science. Series in Computer Science. Prentice Hall, second edition, 1995.
3. Francis Borceux. Handbook of Categorical Algebra, volume 1. Cambridge University Press, 1994.
4. A. Carboni, S. Kasangian, and R. Street. Bicategories of spans and relations. Journal of Pure and Applied Algebra, 33:259–267, 1984.
5. J. R. B. Cockett and D. A. Spooner. SPROC categorically. In CONCUR 94: Fifth Internation Conference on Concurrency Theory, Uppsala, Sweden, Lecture Notes in Computer Science. Springer-Verlag, 1994.