www.ifm.liu.se/~micho/phd/Chapter2.pdf
http://www-centre.mpce.mq.edu.au/alfpapers/a098.pdf
http://www.mevis.de/~anna/publications/goslar.pdf
www.emis.de/journals/SLC/opapers/s30allouche.pdf
iml.univ-mrs.fr/~cassaign/publis/pal7.ps.gz
THE HEIGHWAY DRAGON REVISITED:	http://www.math.nmsu.edu/~nnguyen/23paper.ps