When Nevanlinna earned his doctorate in 1919, there were no university posts available so he became a school teacher. His brother, Frithiof, had received his doctorate in 1918 but likewise was unable to take up a post at a university, and instead began working as a mathematician for an insurance company. Frithiof recruited Rolf to the company, the insurance firm Salama (later
Pohjola Insurance), and Nevanlinna worked approximately twenty hours a week teaching mathematics at a secondary school while simultaneously working as a mathematician for the insurance company, until he was appointed a
Docent of Mathematics at the University of Helsinki in 1922. which contains the Main Theorems was published in 1925 in the journal
Acta Mathematica.
Hermann Weyl has called it "one of the few great mathematical events of the [twentieth] century."{{cite book|author=H. Weyl| author-link=Hermann Weyl|title=Meromorphic functions and analytic curves Nevanlinna theory touches also on a class of functions called the Nevanlinna class, or functions of "
bounded type". When the
Winter War broke out (1939), Nevanlinna was invited to join the
Finnish Army's Ballistics Office to assist in improving
artillery firing tables. These tables had been based on a calculation technique developed by General
Vilho Petter Nenonen, but Nevanlinna now came up with a new method which made them considerably faster to compile. In recognition of his work he was awarded the
Order of the Cross of Liberty, Second Class, and throughout his life he held this honour in especial esteem. From 1947 Nevanlinna had a chair in the
University of Zurich, which he held on a half-time basis after receiving in 1948 a permanent position as one of the 12 salaried Academicians in the newly created
Academy of Finland. Among Rolf Nevanlinna's later interests in mathematics were the theory of
Riemann surfaces (the monograph
Uniformisierung in 1953) and
functional analysis (
Absolute analysis in 1959, written in collaboration with his brother Frithiof). Nevanlinna also published in Finnish a book on the foundations of geometry and a semipopular account of the
Theory of Relativity. His Finnish textbook on the elements of complex analysis,
Funktioteoria (1963), written together with
Veikko Paatero, has appeared in German, English and Russian translations. Rolf Nevanlinna supervised at least 28 doctoral theses. His first and most famous doctoral student was
Lars Ahlfors, one of the first two
Fields Medal recipients. The research for which Ahlfors was awarded the prize (proving the Denjoy Conjecture, now known as the
Denjoy–Carleman–Ahlfors theorem) was strongly based on Nevanlinna's work. Nevanlinna's work was recognised in the form of honorary degrees which he held from several universities: the
University of Heidelberg, the
University of Bucharest, the
University of Giessen, the
Free University of Berlin, the
University of Glasgow, the
University of Uppsala, the
University of Istanbul and the
University of Jyväskylä. He was an honorary member of several learned societies, among them the
London Mathematical Society and the
Hungarian Academy of Sciences. The
1679 Nevanlinna main belt asteroid is named after him. ==Administrative activities==