* {{cite book |author1=Poli, R. |author2=Langdon, W. B. |author3=McPhee, N. F. |year=2008 |title=A Field Guide to Genetic Programming |publisher=Lulu.com, freely available from the internet |url=http://cswww.essex.ac.uk/staff/rpoli/gp-field-guide/ |isbn=978-1-4092-0073-4 |access-date=2011-03-05 |archive-url=https://web.archive.org/web/20160527142933/http://cswww.essex.ac.uk/staff/rpoli/gp-field-guide/ |archive-date=2016-05-27 |url-status=dead }}{{self-published source|date=February 2020}} | * {{cite book |author1=Poli, R. |author2=Langdon, W. B. |author3=McPhee, N. F. |year=2008 |title=A Field Guide to Genetic Programming |publisher=Lulu.com, freely available from the internet |url=http://cswww.essex.ac.uk/staff/rpoli/gp-field-guide/ |isbn=978-1-4092-0073-4 |access-date=2011-03-05 |archive-url=https://web.archive.org/web/20160527142933/http://cswww.essex.ac.uk/staff/rpoli/gp-field-guide/ |archive-date=2016-05-27 |url-status=dead }}{{self-published source|date=February 2020}} |