so that everyone could hear his contribution. Kőnig applied a theorem proved in the thesis of Hilbert's student Felix Bernstein; this theorem, however, was not as generally valid as Bernstein had claimed. Ernst Zermelo, the later editor of Cantor's collected works, found the error already the next day. In 1905 there appeared short notes by Bernstein, correcting his theorem, and Kőnig, withdrawing his claim. Nevertheless, Kőnig continued his efforts to disprove parts of set theory. In 1905 he published a paper that claimed to prove that not all sets could be well-ordered. This statement was doubted by Cantor in a letter to Hilbert in 1906: Cantor was wrong. Today Kőnig's assumption is generally accepted. Contrary to Cantor, presently the majority of mathematicians considers undefinable numbers not as absurdities. This assumption leads, according to Kőnig, Kőnig's conclusion is not stringent. His argument does not rule out the possibility that the continuum can be well-ordered; rather, it rules out the conjunction of "the continuum can be well-ordered by a definition in language L" and "the property of being definable in language L is itself definable in language L". The latter is no longer generally held to be true. For an explanation compare Richard's paradox. The last part of his life Kőnig spent working on his own approach to set theory, logic and arithmetic, which was published in 1914, one year after his death. When he died he had been working on the final chapter of the book. About Kőnig At first Georg Cantor highly esteemed Kőnig. In a letter to Philip Jourdain in 1905 he wrote: Later on Cantor changed his attitude: Some papers and books by Kőnig Zur Theorie der Modulargleichungen der elliptischen Functionen, Thesis, Heidelberg 1870. Ueber eine reale Abbildung der s.g. Nicht-Euclidischen Geometrie, Nachrichten von der Königl. Gesellschaft der Wissenschaften und der Georg-August-Universität zu Göttingen, No. 9 (1872) 157-164. Einleitung in die allgemeine Theorie der Algebraischen Groessen, Leipzig 1903. Zum Kontinuum-Problem , Mathematische Annalen 60 (1905) 177-180. Über die Grundlagen der Mengenlehre und das Kontinuumproblem, Mathematische Annalen 61 (1905) 156-160. Über die Grundlagen der Mengenlehre und das Kontinuumproblem (Zweite Mitteilung), Mathematische Annalen 63 (1907) 217-221. Neue Grundlagen der Logik, Arithmetik und Mengenlehre, Leipzig 1914. Literature and links Brockhaus: Die Enzyklopädie, 20th ed. vol. 12, Leipzig 1996, p. 148. W. Burau: Dictionary of Scientific Biography vol. 7, New York 1973, p. 444. H. Meschkowski, W. Nilson (eds.): Georg Cantor Briefe,