[MathSciNet lists 29 items (out of almost 200) by Paul Cohn that are coded for categories. I've appended Fred Linton's review of one of his earlier categorical papers.] Copyright 2006 Times Newspapers Limited The Times (London) June 29, 2006, Thursday SECTION: FEATURES; Pg. 64 LENGTH: 425 words HEADLINE: Professor Paul Cohn BODY: Professor Paul Cohn, FRS, mathematician, was born on January 8, 1924. He died on April 20, 2006, aged 82. Mathematician who devoted himself to algebra. 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. ********************************************************************** Cohn, P. M. Morita equivalence and duality. Queen Mary College Mathematics Notes Queen Mary College, London, 1968 ii+79 pp. These notes provide an introduction to, and an exposition of, the ideas of Morita, Bass, Chase, Schanuel, et al., regarding the question, to be answered in terms of the ground ring, of what module categories are equivalent, respectively dual, to each other. The main goal is to provide a good presentation of the equivalence theory; to this end, the notes of Hyman Bass ["The Morita theorems", mimeographed notes, Univ. of Oregon, Eugene, Ore., 1962; see also Algebraic $K$-theory, Chapter II, Benjamin, New York, 1968; MR0249491 (40 \#2736)] are relied upon fairly heavily. A preliminary goal is to develop enough category theory to get by with; the development is in fact very rapid, though not too sketchy, but a little misleading or garbled in places (examples: the functor of the exercise on page 8 is contravariant and goes elsewhere than is there stated; the first two examples of equivalences of categories, presented on page 7 after a brief sermon on the advantages of the notion of equivalence over that of isomorphism, turn out, despite the readily inferred implication to the contrary, to be in fact isomorphisms; the choice of the term "homotopy inverse" to describe an inverse equivalence seems ill advised). A subsidiary goal is the duality question, which receives an adequately careful treatment and is used to open up the related area of quasi-frobeniosity. Reviewed by F. E. J. Linton