1. Aristotle, De Anima, I, 4, 409, a4; T. L. Heath's Thirteen Books of Euclid, vol. 1, 2nd edition (1926), p. 170.
2. William Hawney, The Complete Measurer, ninth Edition (1755), p. 159. See also p. 154. (First edition, London, 1717).
3. Beiträge zur Theorie der Minimalflächen