Who did more ring theory, Cahit Arf or Sind ibn Ali?
Cahit Arf Cahit Arf (] ; 11 October 1910 – 26 December 1997) was a Turkish mathematician. He is known for the Arf invariant of a quadratic form in characteristic 2 (applied in knot theory and surgery theory) in topology, the Hasse–Arf theorem in ramification theory, Arf semigroups, and Arf rings.
Hasan ibn Zayd Al-Ḥasan ibn Zayd ibn Muḥammad ibn Ismā‘il ibn al-Ḥasan ibn Zayd (Arabic: الحسن بن زيد بن محمد‎ ‎ ; died 6 January 884), also known as al-Da‘ī al-kabīr (Arabic: داعي الكبير‎ ‎ , "the Great/Elder Missionary"), was an Alid who became the founder of the Zaydid dynasty of Tabaristan.