1. G. Fagnano, Collected Works, Especially vol. 2, papers XXXII, XXXIII and XXXIV.
2. John Bernoulli, Collected Works, vol. 3, lecture 34 of item CXLIX.
3. C. L. Siegel, Collected Works, vol. 3, pp. 249–251. See also Sammelband Leonhard Euler, Akademie Verlag Berlin 1959.
4. James Bernoulli, Collected works, vol. 1, 576–600.
5. L. Euler, Collected works, series 2, vol. 10, pp. 1–17.