1. Barricelli NA (1954) Esempi numerici di processi di evoluzione. Methodos, pp 45–68
2. Butler S (1872) Erewhon: or over the range. Jonathan Crane (1921), London, p 252
3. Butler S (1880) Unconscious memory
4. Copeland J (2000) Turing’s last programs.
http://www.alanturing.net/turing_archive/pages/Reference%20Articles/Turing%27s%20last%20programs.html
. Accessed 14 Sept 2010
5. Gardener M (1970) Mathematical games. Scient Am