Felix Klein (1893). “The Evanston Colloquium: Lectures on Mathematics Delivered from Aug. 28 to Sept. 9, 1893 Before Members of the Congress of Mathematics Held in Connection with the World's Fair in Chicago at Northwestern University, Evanston, Ill”

Felix Klein (1922). “Gesammelte mathematische Abhandlungen: Zur anschaulichen Geometrie. Zur AuflÃ¶sung algebraischer Gleichungen. Physikalisches. Hrsg. von R. Fricke und H. Vermeil”

Felix Klein (1893). “The Evanston Colloquium: Lectures on Mathematics Delivered from Aug. 28 to Sept. 9, 1893 Before Members of the Congress of Mathematics Held in Connection with the World's Fair in Chicago at Northwestern University, Evanston, Ill”