Albert Einstein (2015). “Bite-Size Einstein: Quotations on Just About Everything from the Greatest Mind of the Twentieth Century”, p.40, St. Martin's Press
Thomas Jefferson (2011). “The Papers of Thomas Jefferson, Retirement Series, Volume 7: 28 November 1813 to 30 September 1814”, p.248, Princeton University Press
"Christianity: the One, the Many: What Christianity Might Have Been and Could Still Become, Volume 1". Book by John F. Nash (p. 11), February 14, 2008.