Peter Ferdinand Drucker (2006). “Classic Drucker: Essential Wisdom of Peter Drucker from the Pages of Harvard Business Review”, p.195, Harvard Business Press
Mark Twain (1870). “The Innocents Abroad, Or, The New Pilgrims' Progress: Being Some Account of the Steamship Quaker City's Pleasure Excursion to Europe and the Holy Land : with Descriptions of Countries, Nations, Incidents and Adventures, as They Appeared to the Author”, p.650
Frederick Douglass, Solomon Northup, Willie Lynch, Nat Turner, Sojourner Truth (2017). “100$ REWARD ON MY HEAD – Powerful & Unflinching Memoirs Of Former Slaves: 28 Narratives in One Volume: With Hundreds of Documented Testimonies & True Life Stories: Memoirs of Frederick Douglass, Underground Railroad, 12 Years a Slave, Incidents in Life of a Slave Girl, Narrative of Sojourner Truth...”, p.1065, e-artnow