1. T. W. De Bakker and D. A. Scott, ?A theory of programs: unpublished notes,? in: IBM Seminar, Vienna (1969).
2. A. P. Ershov, ?The current state of the theory of program schemes,? in: Cybernetics Problems [in Russian], No. 27, Nauka, Moscow (1973).
3. A. P. Ershov, ?On-line algorithms. Part 3,? in: Cybernetics Problems [in Russian], No. 20, Nauka, Moscow (1968).
4. Yu. I. Yanov, ?Local transformations of algorithm schemes,? in: ibid.
5. V. K. Sabel'fel'd, ?Transformations of unary linear recursive schemes,? Kibernetika, No. 5 (1975).