Cahit Arf

Cahit Arf (1910–1997) was a Turkish mathematician whose name is carried by the Arf invariant, the Hasse–Arf theorem, and Arf rings and semigroups. Born in Thessaloniki and educated in Paris and Göttingen, he became one of the central figures of modern mathematics in Turkey: a professor at Istanbul University and the Middle East Technical University, the founding director of the Turkish Scientific and Technical Research Council (TÜBİTAK), and the face on the Turkish ten-lira note issued in 2009. ¹

He was born in Thessaloniki, then in the Ottoman Empire, in 1910 — the Turkish article and the English article's body give 11 October 1910, while the English article's lead gives 24 October, the Gregorian equivalent of the same day. His family moved to Istanbul and then to Izmir during his childhood. A scholarship took him to Paris, where he studied at the École Normale Supérieure, and then to Göttingen, where he completed his doctorate in 1938 under Helmut Hasse. ^{1 2}

His doctoral work produced what is now called the Arf invariant of a quadratic form, and with Hasse the Hasse–Arf theorem in class field theory; his later work extended to Arf semigroups and rings. After his doctorate he taught at Galatasaray and at Istanbul University, and spent 1964–66 at the Institute for Advanced Study in Princeton. In 1963 he became the founding director of TÜBİTAK, the body that organised state support for science in Turkey. He joined the Middle East Technical University in Ankara and taught there until his retirement in 1980, training a generation of Turkish mathematicians. ¹

He died on 26 December 1997 at Bebek in Istanbul, and was buried in the city's Zincirlikuyu Cemetery. Turkey placed his portrait on the ten-lira note of 2009, and his name is carried by a mathematics symposium and by institutions in Turkey; the invariant that bears his name remains a standard tool in topology and algebra. ^{1 2}

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