Horning, J. J. "Some desirable properties of data abstraction facilities" pp60-62

[SIGPLAN] (1976) SIGPLAN Notices 11(02) February 1976 also Proceedings of the SIGPLAN '76 Conference on Data: Abstraction, Definition and Structure, Salt Lake City, Utah, USA, March 22-24, 1976  

Languages mentioned Alphard {1974} Pascal with data abstraction CLU {1974} CLUster programming language - abstractions and iterators Euclid {1977} Verifiable system software language