He conjectured the Koebe quarter theorem on the radii of disks in the images of injective functions, in 1907. His conjecture became a theorem when it was proven by Ludwig Bieberbach in 1916, and the function providing a tight example for this theorem became known as the Koebe function.[2]
^Duren, Peter L. (1983), Univalent functions, Grundlehren der Mathematischen Wissenschaften [Fundamental Principles of Mathematical Sciences], vol. 259, Springer-Verlag, New York, pp. 30–31, ISBN0-387-90795-5, MR0708494
^"Notes". Bulletin of the American Mathematical Society. 29 (5). Providence, Rhode Island: American Mathematical Society: 235. May 1923. doi:10.1090/S0002-9904-1923-03715-4.