Zachary Taylor, S. HORN (1848). “All the Letters of Major General Z. Taylor: Anecdotes of rough and ready: Songs of Old Zach's Campaigns, etc. [Edited by] S. Horn”, p.10
"Mathematical Games". Scientific American (October 1973), later quoted in Roger B. Nelson "Proofs Without Words: Exercises in Visual Thinking" ("Introduction", p. 5), 1993.