1. S. Awodey, J. Hughes, The coalgebraic dual of Birkhoff's variety theorem, Tech. Report CMU-PHIL-109, Carnegie Mellon University, Pittsburgh, PA, 15213, November 2000.
2. J. Barwise, L. Moss, Vicious Circles, CSLI Lecture Notes, Standford University, Standford, CA, 1996.
3. Introduction to extensive and distributive categories;Carboni;J. Pure Appl. Algebra,1993
4. Introduction to distributive categories;Cockett;Math. Struct. Comput. Sci.,1993
5. J. Gibbons, Lecture Notes on Algebraic and Coalgebraic Methods for Calculating Functional Programs, Estonian Winter School on Computer Science, 1999.