1. J. A. Goguen, J. W. Thatcher, E. G. Wagner, An initial algebra approach to the specification, correctness and implementation of abstract data types, in: R. T. Yeh (ed.): Current trends in programming methodology, Vol. 4, Data structuring, pp. 80–149 (Prentice-Hall, Englewood Cliffs, 1978)
2. F. L. Bauer: Programming as fulfilment of a contract, in: P. Henderson (ed.): System design, Infotech: State of the Art Report 9:6, pp. 165–174 (Pergamon Infotech Ltd., Maidenhead, 1981)
3. M. Breu: Development of implementations, in: PROgram Development by SPECification and TRAnsformation, Volume I, PROSPECTRA — Esprit Project Number 390, Report M2.2.S4 — R — 11.0, 1990 (to appear in LNCS)
4. M. Breu: Endliche Implementierung algebraischer Spezifikationen, Ph.D. Thesis (in German), technical report TUM 19111, Institut für Informatik, TU München, (1991)
5. M. Broy, M. Wirsing: Partial abstract types, Acta Informatica 18, pp. 47–64(1982)