T. Colin Campbell, Thomas M. Campbell (II.) (2006). “The China Study: The Most Comprehensive Study of Nutrition Ever Conducted and the Startling Implications for Diet, Weight Loss and Long-term Health”, p.106, BenBella Books
"Aesthetics and the Environment: The Appreciation of Nature, Art and Architecture". Book by Allen Carlson, Routledge, London & New York, p. 118, "Abstract Art, Concrete Art", 2005.