G. Pomberger, H. Mössenböck, and P. Rechenberg. The School of Niklaus Wirth: The Art of Simplicity, page 5--20. Heidelberg, dpunkt.verlag, (October 2000)http://www.swe.uni-linz.ac.at/publications/pdf/TR-SE-00.08.pdf
-- last visited: $17^th$~January~2009.