1. da Vinci L. Manuscript RL 19115v; K/P 114r located in the Royal Library, Windsor Castle, Windsor, England, ca. 1500.
2. Papanek V. The green imperative. New York: Thames and Hudson, 1995.
3. Grove N. Recycling, National Geographic. Washington DC: National Geographic Society, July 1994:92–115.
4. Graves W, editor. Water: the power, promise, and turmoil of North America's water. National Geographic (special edn.), Washington DC: National Geographic Society, November 1993.
5. Mackenzie D. Design for the environment. New York: Rizzoli International Publications, 1991.