"Incoming Presidential Speech: International Society for the Systems Sciences 43rd Annual Meeting" by Peter Corning, complexsystems.org. June 02, 2015.
Smithsonian Institution, John Wesley Powell, Almon Harris Thompson, Elliott Coues, George Brown Goode (1875). “Exploration of the Colorado River of the West and Its Tributaries: Explored in 1869, 1870, 1871, and 1872, Under the Direction of the Secretary of the Smithsonian Institution”, p.55