References  1.  N. Wirth, "The  Programmin~  Language Pascal,"  Acta Informatica,  1,35-63, 1971.  2.  N.  Wirth,  "Program  Deve opment  by  Stepwise  Refinement,"  Communications of the ACM,  P, 221-227, April 1971.  3.  N. Wirth,  Systematic Programming,  Prentice-Hall, Inc., 1973.  4.  O.J. Dahl, E.W. Dijkstra, C.A.R. Hoare,  Structured Programming,  Academic Press Inc., 1972.  5.  c.A.R.  Hoare and N.  Wirth. "An Axiomatic Definition of the  Programming Language Pascal,"  Acta Informatica,  2, 335-355,1973.  6.  D.E.  Knuth,  The  Art  oj  Computer  Programming,  Vol  1,  Fundamental Algorithms,  Addi~  1.1I1-Wesley, 1968.  7.  N. Wirth, "An Assessment 0  the Programming Language Pascal,"  SIGPLAN Notices,  10,23-30, Jill!.? 1975.  202 