William Damon (2014). “Failing Liberty 101: How We Are Leaving Young Americans Unprepared for Citizenship in a Free Society”, p.3, Hoover Institution Press
Herbert Hoover, Arnold S. Rice, United States. President (1929-1933 : Hoover) (1971). “Herbert Hoover, 1874-1964; chronology-documents-bibliographical aids”, Oceana Pubns
Hannah Arendt (1972). “Crises of the Republic: Lying in Politics; Civil Disobedience; On Violence; Thoughts on Politics and Revolution”, p.17, Houghton Mifflin Harcourt
Caleb Scharf (2012). “Gravity's Engines: How Bubble-Blowing Black Holes Rule Galaxies, Stars, and Life in the Cosmos”, p.187, Scientific American / Farrar, Straus and Giroux