Cohn was the only child of Jewish parents, James (or Jakob) Cohn, owner of an import business, and Julia (née Cohen[6]), a schoolteacher.[5][7]
Both of his parents were born in Hamburg, as were three of his grandparents. His ancestors came from various parts of Germany. His father fought in the German army in World War I; he was wounded several times and awarded the Iron Cross.[7] A street in Hamburg is named in memory of his mother.[8]
When he was born, his parents were living with his mother's mother in Isestraße. After her death in October 1925, the family moved to a rented flat in a new building in Lattenkamp, in the Winterhude quarter. He attended a kindergarten then, in April 1930, moved to Alsterdorfer Straße School. After a while, he had a new teacher, a National Socialist, who picked on him and punished him without cause. Thus in 1931, he moved to the Meerweinstraße School where his mother taught.[7]
Following the rise of the Nazis in 1933, his father's business was confiscated and his mother dismissed. He moved to the Talmud-Tora-Schule, a Jewish school. In mid-1937, the family moved to Klosterallee. This was nearer the school, the synagogue and other pupils, being in the Jewish area. His German teacher was Dr. Ernst Loewenberg, the son of the poet Jakob Loewenberg.[7]
On the night of 9/10 November 1938 (Kristallnacht), his father was arrested and sent to Sachsenhausen concentration camp. He was released after four months but told to emigrate. Cohn went to Britain in May 1939 on the Kindertransport to work on a chicken farm, and never saw his parents again. He corresponded regularly with them until late 1941. At the end of the War, he learned that they were deported to Riga on 6 December 1941 and never returned. At the end of 1941, the farm closed. He trained as a precision engineer, acquired a work permit and worked in a factory for 4½ years. He passed the Cambridge Scholarship Examination, and won an exhibition to Trinity College, Cambridge.[5][7]
In the early 1980s, funding cuts caused the closure of the small colleges of the University of London. Cohn moved to University College London in 1984,[10] together with the two other experts at Bedford on ring theory, Bill Stephenson and Warren Dicks.[11] He became Astor Professor of Mathematics there in 1986. He continued to be a visiting professor, for example to the University of Alberta in 1986 and to Bar Ilan University in 1987. He retired in 1989, but remained active as professor emeritus and honorary research fellow until his death.[3][5]
He was president of the London Mathematical Society, 1982–1984, having been its secretary, 1965–1967 and a council member in 1968–1971, 1972–1975 and 1979–1982. He was editor of the society's monographs in 1968–1977 and 1980–1993. He was elected a Fellow of the Royal Society in 1980 and was on its council, 1985–1987. He was a member of the Mathematical Committee of the Science Research Council, 1977–1980.[3] He chaired the National Committee for Mathematics, 1988–1989.[4]
In 1957 Cohn published his first book, Lie Groups, on groups that are analytic manifolds: Lie groups. His second book, Linear Equations, appeared in 1958 and his third, Solid geometry, in 1961. Universal algebra appeared in 1965 (second edition 1981). After that, he concentrated on non-commutative ring theory and the theory of algebras.[3] His monograph Free Rings and their Relations appeared in 1971. It covered the work of Cohn and others on free associative algebras and related classes of rings, especially free ideal rings. He included all of his own published results on the embedding of rings into skew fields. The second, enlarged edition appeared in 1985.[3]
Cohn also wrote undergraduate textbooks. Algebra I appeared in 1974 and Algebra II in 1977. The second edition, in three volumes, was published by Wiley between 1982 and 1991.[3] These volumes were in line with the British (rather than American) curricula at the time and include both linear algebra and abstract algebra. Cohn wrote a subsequent revised iteration of the first volume as Classical Algebra (Wiley, 2000) as a more "user friendly" version for undergraduates (according to its preface); this book also includes a few selected topics from volumes II and III of Algebra.
The final incarnation of Cohn's algebra textbooks appeared in 2003 as two Springer volumes Basic Algebra and Further Algebra and Applications. The material in Basic Algebra is (according to its preface) rather more concise and, while corresponding roughly with Algebra I, assumes knowledge of linear algebra. The material on basic theories (groups, rings, fields) is pursued in more depth in Basic Algebra compared to Algebra I. Further Algebra and Applications roughly corresponds to volumes II and III of Algebra, but reflects the shift of some material from these volumes to Basic Algebra.
Private life
His recreation was etymology and language in all its forms. He married Deirdre Sharon in 1958, and they had two daughters.[4][6]
Cohn, Paul; Struan Robertson (website owner) (February 2003). "Paul M. Cohn, (Childhood in Hamburg)"(Autobiography). A History of Jews in Hamburg: The Kindertransports. Retrieved 24 July 2008.
