Thébault’s theorem, discovered in 1938 (see ), has the remarkable property that it required three decades to obtain a ﬁrst proof, which then took 24 pages of calculations. Subsequent shorter proofs, but not easy ones, were published mainly in Elemente der Mathematik ( and ) and in Dutch language. We refer to , , and  for complete accounts of all these and recent proofs. In this note we want to emphasize the role of a certain parabola which comes out of a dynamic machine, and which allows an easy understanding.
Cite this article
Gerhard Wanner, Alexander Ostermann, A dynamic proof of Thébault’s theorem . Elem. Math. 65 (2010), no. 1, pp. 12–16DOI 10.4171/EM/133