Albert Einstein (2015). “Bite-Size Einstein: Quotations on Just About Everything from the Greatest Mind of the Twentieth Century”, p.52, St. Martin's Press
Albert Einstein (2015). “Bite-Size Einstein: Quotations on Just About Everything from the Greatest Mind of the Twentieth Century”, p.31, St. Martin's Press
"The 100 best nonfiction books: No 68 - Narrative of the Life of Frederick Douglass, an American Slave by Frederick Douglass (1845)" by Robert McCrum, www.theguardian.com. May 22, 2017.
Socrates, Plato, Aristotle (1967). “Wit and Wisdom of Socrates, Plato, Aristotle: Being a Treasury of Thousands of Glorious, Inspiring and Imperishable Thoughts, Views and Observations of the Three Great Greek Philosophers, Classified Under about Four Hundred Subjects for Comparative Study”