Richard C. Holt, David B. Wortman. A sequence of structured subsets of PL/I. In Douglas S. Kerr, editor, Proceedings of the 4th SIGCSE Technical Symposium on Computer Science Education, SIGCSE 1974, Detroit, MI, USA, February 14-15, 1974. pages 129-132, ACM, 1974. [doi]
Abstract is missing.