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Albert Einstein (2015). “Bite-Size Einstein: Quotations on Just About Everything from the Greatest Mind of the Twentieth Century”, p.15, St. Martin's Press
Albert Einstein, Harry Woolf (1980). “Some strangeness in the proportion: a centennial symposium to celebrate the achievements of Albert Einstein”, Addison Wesley Publishing Company
Albert Einstein (2015). “Bite-Size Einstein: Quotations on Just About Everything from the Greatest Mind of the Twentieth Century”, p.32, St. Martin's Press