Clark, B. L.; and Horning, J. J. "Reflections on a language designed to write an operating system" pp52-56

[SIGPLAN] (1973) SIGPLAN Notices 8(09) June 1973 Proceedings of ACM SIGPLAN - SIGOPS interface meeting on Architectural Support for Programming Languages and Operating Systems, Savannah, Georgia, 1973  

Languages mentioned Sue {1971}