Julius König

Julius König, known in Hungary as Gyula Kőnig (1849 to 1913), was a Hungarian mathematician who worked on algebra, number theory, geometry, set theory and analysis. Born in Győr, he began by studying medicine in Vienna, then turned to mathematics under the influence of Hermann von Helmholtz and Leo Königsberger, and took his doctorate at Heidelberg in 1870 with a thesis on the modular equations of elliptic functions. He became a docent at Budapest in 1872 and a full professor at the Technical University of Budapest in 1874, where he raised the level of mathematics teaching, served as dean and as rector, and was elected to the Hungarian Academy of Sciences. In August 1904 he announced at the International Congress of Mathematicians in Heidelberg that the continuum hypothesis was false; the proof contained an error, but the episode led him to the paradox now named after him, about a number that is and is not finitely definable. His book on the foundations of logic, arithmetic and set theory was completed by his son Dénes Kőnig and published after his death.