Thomas Jefferson (1854). “The writings of Thomas Jefferson: being his autobiography, correspondence, reports, messages, addresses, and other writings, official and private”, p.506
Charles Babbage, Philip Morrison, Emily Morrison (1961). “Charles Babbage on the Principles and Development of the Calculator: And Other Seminal Writings”, p.322, Courier Corporation
"Pedro Almodóvar Talks I’M SO EXCITED, the Role of Sex and Death in His Work, Making the “Gayest Film” He’s Done in 20 Years, and More". Interview with Sheila Roberts, collider.com. June 24, 2013.