Jakob Nielsen (15 October 1890 in Mjels,

2011 pbk edition

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Als
Amyotrophic lateral sclerosis (ALS; also known as Lou Gehrig's disease in Canada
Canada is a country in the northern part of North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the A ...

– 3 August 1959 in Helsingør
Helsingør ( , ; sv, Helsingör), classically known in English as Elsinore , is a city in eastern Denmark. Helsingør Municipality had a population of 62,686 on 1 January 2018. Helsingør and Helsingborg in Sweden together form the northern re ...

) was a Danish mathematician
A mathematician is someone who uses an extensive knowledge of mathematics
Mathematics (from Greek: ) includes the study of such topics as numbers (arithmetic and number theory), formulas and related structures (algebra), shapes and spaces ...

known for his work on automorphism
In mathematics
Mathematics (from Greek: ) includes the study of such topics as numbers (arithmetic and number theory), formulas and related structures (algebra), shapes and spaces in which they are contained (geometry), and quantities and t ...

s of surface (mathematics), surfaces. He was born in the village Mjels on the island of Als Island, Als in North Schleswig, in modern-day Denmark. His mother died when he was 3, and in 1900 he went to live with his aunt and was enrolled in the Realgymnasium. In 1907 he was expelled for membership to an illicit student club. Nevertheless, he matriculated at the University of Kiel in 1908.
Nielsen completed his doctoral dissertation in 1913. Soon thereafter, he was drafted into the German Imperial Navy. He was assigned to coastal defense. In 1915 he was sent to Constantinople as a military adviser to the Ottoman Empire, Turkish Government. After the war, in the spring of 1919, Nielsen married Carola von Pieverling, a German medical doctor.
In 1920 Nielsen took a position at the Technical University of Breslau. The next year he published a paper in Mathematisk Tidsskrift in which he proved that any subgroup of a finitely generated free group is free. In 1926 Otto Schreier would generalize this result by removing the condition that the free group be finitely generated; this result is now known as the Nielsen–Schreier theorem. Also in 1921 Nielsen moved to the Royal Veterinary and Agricultural University in Copenhagen, where he would stay until 1925, when he moved to the Technical University of Denmark, Technical University in Copenhagen.
He also proved the Dehn–Nielsen theorem on mapping class groups.
Nielsen was a Plenary Speaker of the International Congress of Mathematicians, ICM in 1936 in Oslo.
During World War II some efforts were made to bring Nielsen to the United States as it was feared that he would be assaulted by the Nazis. Nielsen would, in fact, stay in Denmark during the war without being harassed by the Nazis.
In 1951 Nielsen became professor of mathematics at the University of Copenhagen, taking the position vacated by the death of Harald Bohr. He resigned this position in 1955 because of his international undertakings, in particular with UNESCO, where he served on the executive board from 1952 to 1958.
Bibliography

2011 pbk edition

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See also

* Fenchel–Nielsen coordinates * Nielsen transformation * Nielsen theory * Nielsen–Thurston classification * Nielsen realization problemReferences

External links

* * {{DEFAULTSORT:Nielsen, Jakob 1890 births 1959 deaths 20th-century mathematicians Danish mathematicians People from Sønderborg Municipality