1. "The island of Texel towards a sustainable energy future" (20/12/2014):
2. "Hierarchy of Societal Needs" (1/12/2011):
https://gaianomy.wordpress.com/2011/12/04/hierarchy-of-social-needs-by-gaianomy-at-last/
3. "Criteria of Sustainability" (1998):
http://www.holocene.net/sustainability/sustainability.htm
