Professor Frank Bonsall, DSc, FRS, FRSE.

Distinguished mathematician who contributed to the debate on Munro definitions

Frank Bonsall, Emeritus Professor of Mathematics at the University of Edinburgh, was a distinguished mathematician and a significant figure in the mathematical life of the United Kingdom in the post-war years, particularly in Scotland and the north of England. His family moved to Welwyn Garden City in 1923, where Frank attended Fretherne House Preparatory School before moving on to Bishops Stortford College. He went up to Merton College, Oxford in 1938 to read mathematics.

He later recalled how much he enjoyed the freedom of university life during that first year at Oxford, as well as his first encounters with rigorous analysis, the area of mathematics that was to become his speciality. His university career was interrupted by war service in the Royal Engineers from 1940 to 1946. The final two years of this were spent in India testing equipment under jungle conditions.

He returned to Oxford, graduating with First Class Honours, and met a fellow mathematics undergraduate, Gillian (Jill) Patrick; they married in 1947. He could have stayed on at Oxford as a graduate student but decided instead to accept a one-year temporary lectureship at the University of Edinburgh. The following year, he moved to a lectureship at Newcastle where, encouraged by Prof WW Rogosinski, he made a start in research. As a self-taught research mathematician, he benefited greatly from Rogosinski's influence. His early research was along fairly classical lines but he was soon attracted to more abstract analysis.

This interest was reinforced when he spent the academic year 1950-51 with a strong research group at Stillwater, Oklahoma. There, he had his first opportunity for the serious study of functional analysis, a subject that unifies different parts of mathematical analysis within a single more abstract framework and which was to be the focus of his research for the rest of his life.

He was appointed to the chair at Newcastle in 1959 when Rogosinski retired but returned to the University of Edinburgh in 1965 to the newly created McLaurin Chair.

He built up active groups in functional analysis at both Newcastle and Edinburgh, supervising numerous research students and doing much to strengthen the position of the subject more generally across the UK. Of particular note was the key role he played in founding the North British Functional Analysis Seminar, one of the first inter-university seminars in mathematics, and a model for many others. He also took undergraduate teaching seriously; countless former students will remember his lectures for their elegance and lucidity.

The characteristic of Bonsall's research work was its aesthetic simplicity. His interests were wide and his contributions as significant as they were influential. They were recognised in his election to the Royal Society of Edinburgh in 1966 and to the Royal Society in 1970.

He was awarded the Senior Berwick Prize of the London Mathematical Society in 1966 and was president of the Edinburgh Mathematical Society in 1976-77. He never sought committee work but took such work seriously when it came his way. Over the years, he served on the council of the London Mathematical Society, committees of the Royal Society and the Science Research Council, and on numerous editorial boards.

Beyond mathematics, Bonsall had a great interest in mountain climbing, ascending his 280th Munro in 1977. He also contributed to the debate as to when two close tops count as separate Munros (that is, as separate mountains of height at least 3,000 feet). In two articles in the Scottish Mountaineering Club Journal (SMC) in 1973 and 1974, Bonsall developed a rule for determining this. His rule yields a list very close to the original one compiled by Sir Hugh Munro in 1891 and has influenced some subsequent revisions of SMC's definitive list.

When Bonsall retired in 1984, he and Jill moved to Harrogate, where he had more time to devote to gardening, his other great interest. His garden was described by one friend as no less than spectacular. At the same time, he maintained his interest in mathematics, attending seminars at the University of Leeds, where he was an Honorary Fellow, and at the University of York, which awarded him an honorary degree in 1990.

The flow of research papers continued for some years, the last appearing in 2000, just two years before he and Jill moved into a retirement home.

Frank Bonsall was a gifted mathematician for whom his students and colleagues had respect and affection in equal measure. He is survived by his wife.

Alastair Gillespie

Professor Frank Bonsall, DSc, FRS, FRSE. Born: 31 March, 1920, in London. Died: 22 February, 2011, in Harrogate, aged 90.

7 April 2011 Scotsman