## Professor Paul Cohn

### Mathematician who devoted himself to algebra

Professor Paul Cohn, FRS, mathematician, was born on January 8, 1924. He died on April 20, 2006, aged 82.PAUL COHN was a distinguished algebraist and the former Astor Professor of Mathematics at University College London.

An only child, he was born in Hamburg in 1924 to Jewish parents. At 15 he was sent to England on the Kindertransport, and never saw the rest of his family again.

After four years' manual labour, during which he taught himself Latin, he won an exhibition to Trinity College, Cambridge, in 1944. He obtained his BA in 1948 and his PhD, working with Philip Hall at Cambridge, in 1951. After a year as a charge de recherches at the University of Nancy, he served as a lecturer in the University of Manchester (whose mathematics department rivalled that of Cambridge in the early postwar years) from 1952 to 1962.

The rest of his career was in London: as Reader at Queen Mary College, 1962 67, and as professor and head of department at Bedford College, 1967-84. The funding cuts of the early 1980s led to the closure of the small colleges of the University of London. Cohn left the Regent's Park campus of Bedford College for University College, where he was Astor Professor from 1986 till his retirement in 1989.

In addition to many visiting appointments he was elected Fellow of the Royal Society in 1980, and served as president of the London Mathematical Society, 1982-84.

Cohn was a pure mathematician, whose extensive work was devoted to algebra. His particular speciality was ring theory -the study of mathematical structures in which, as with ordinary numbers, one can add, subtract and multiply, but not necessarily divide -and in particular, non-commutative ring theory. Here, the order in which one multiplies matters, unlike multiplication of ordinary numbers, but as with the multiplication of matrices.

Cohn wrote nearly 200 mathematical papers, over more than 50 years. He also wrote ten books, including the classic *Algebra* -this appeared first as two volumes (1974-77), split into three (1982-91), and finally reappeared as two again *Basic Algebra* and *Further Algebra* (2003). His best-known research monograph was *Free Rings and Their Relations* (1971).

Cohn wrote on number theory as well as his beloved algebra, and was at home in French, German and Russian.

He read widely and developed a particular interest in German history, the background to his early troubles, of which he would talk freely.

He married Deirdre Sonia Sharon in 1958; she survives him, with their two daughters.

June 29, 2006 Copyright (C) The Times, 2006