1. (JAG,JWT,ECW) J.A.Goguen, J.W.Thatcher, E.G.Wagner "An initial algebra approach to the specification, correctness, and implementation of abstract data types" IBM Research Report RC-6487, October 1976.
2. (JAG) J.A.Goguen "Abstract errors for abstract data types". UCLA Semantics Theory of Computation Report 6, February 1977. Proceedings IFIP Working Conference on Formal Description of Programming Concepts. St. Andrews, New Brusswick, pp. 21.1–21.32. August 1977.
3. R.M. Burstall and J.A.Goguen "Putting Theories together to make Specifications". Proceedings 1977 IJCAI,MIT, Cambridge, MA, August 1977.
4. H.Ehrig, H.J.Kreowski and P.Padawitz "Stepwise specification and implementation of abstract data types". Technical University of Berlin, Report, March 1978.
5. R.Fateman "Essays in algebraic simplification". Ph.D. diss, Harward U., Cambridge, Mass., 1971.