Coba jelasin Catatan dari Piet Hein dong

Gardner, Martin: Piet Hein's Superellipse. – in Gardner, Martin: Mathematical Carnival. A New Round-Up of Tantalizers and Puzzles from Scientific American. New York: Vintage, 1977, pp. 240–254.

Johan Gielis: Inventing the circle. The geometry of nature. – Antwerpen : Geniaal Press, 2003. –

"A Poet with a Slide Rule: Piet Hein Bestrides Art and Science," by Jim Hicks, Life Magazine, Vol. 61 No. 16, 10/14/66, pp. 55–66

"Piet Hein Biographical Details", by Nils Aas, tr. by Roger Stevenson. The Papers of the Medford Educational Institute 3.

"To and by Piet Hein on the Occasion of Piet Hein's Election as the Student Organization's Twelfth Honorary Member", tr. by Roger Stevenson. The Papers of the Medford Educational Institute 2.