Mark Twain, Michael Barry Frank, Robert Pack Browning, Lin Salamo, Frederick Anderson, Mark Twain (1980). “Mark Twain's Notebooks & Journals, Volume III: (1883-1891)”, p.172, Univ of California Press
Mark Twain (2014). “Mark Twain on Common Sense: Timeless Advice and Words of Wisdom from America's Most-Revered Humorist”, p.54, Skyhorse Publishing, Inc.