1. F. Klein, (a) Vorträge über ausgewählte Fragen der elementar Geometrie, ausgearbeitet von F. Tägert. Leipzig, Teubner, 1895, 66 pp. +2 Tafeln. (b) Famous Problems of Elementary Geometry… authorized translation of F. Klein's Vorträge…, by Wooster Woodruff Beman and David Eugene Smith. Boston, Ginn, 1897, ix+80 pp. (c) Leçons sur certaines questions de géométrie élémentaire… rédaction Française autorisée par l'auteur, par J. Griess. Paris, Vuibert, 1896, 100 pp. There was also an Italian edition published at Turin in 1896, and a Russian edition which appeared in Kasan in 1898.
2. Disquisitiones arithmeticæ, Lipsiæ, 1801, Werke, Bd. 1,2, abdruck 1870, p. 462; French ed. Recherches Arithmétiques, Paris, 1807, p. 488; Ger. ed. by Maser, Berlin, 1889, p. 447.
3. On the number of inscriptible regular polygons