APersonIndependent states
Cahit Arf
Mathematician (1910–1997) after whom the Arf invariant, Arf rings and the Hasse–Arf theorem are named.
Cahit Arf was born in Salonica and studied in Paris and Göttingen, where he earned his doctorate under the eminent mathematician Helmut Hasse.
The Arf invariant, introduced in his 1941 work on quadratic forms, later found wide use in topology and coding theory. Arf rings and the Hasse–Arf theorem in algebra and number theory also bear his name.
Arf taught at Istanbul University and later at the Middle East Technical University in Ankara and chaired TÜBİTAK's science board. The back of the 10-lira banknote issued in 2009 shows his portrait and the formula of the Arf invariant.
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Updated: October 2, 2026