My father, Dr David Rees, who has died aged 72, was a polymath whose intelligence shone out throughout his life. Dai, as he was known to all, worked at various times as a teacher of maths and statistics, for the Open University, and for the US company National Semiconductor. In the 1980s he settled in Munich, and in 1989 joined the European Patent Office. He worked his way up the organisation, becoming chairman of a board of appeal in 2008.
At the EPO he wrote a decision (G3/08) on the patentability of computer-related inventions. A reference to Lewis Carroll’s Through the Looking Glass in the reasons for the decision was typical of Dai. The decision was well-received, drew worldwide press attention and has its own Wikipedia page.
Both Dai’s parents were talented mathematicians with interests in science. His father Basil was based at the Bristol Aeroplane Company at the time of Dai’s birth in the city. Dai’s mother, Joan (nee Rees), was a secondary schoolteacher for maths and physics, advancing to be a deputy head. His younger brother, Gareth, went on to work in engineering.
Dai attended grammar schools in Kingston upon Thames and Watford. Along with his clear abilities in mathematics, he had very broad talents and interests: he learned Russian, German and French; he played hockey; he took up classical guitar at the age of 10, and later the saxophone and bassoon. His membership of the Scouts instilled a habit of always carrying a Swiss army knife, which could cause problems at airports.
In 1968 he went to Cambridge University to study maths at Jesus College. He relished the intellectual challenge and met a great group of friends; together they became the William Frend Society, named after the late-18th-century social reformer and radical fellow of Jesus College.
After graduating, Dai attended the University of Keele, going on to teach maths and statistics. At Keele he met Sally Witts; they married in 1973 and I was born in 1978. During this time Dai started a postgraduate research programme to write his PhD on algebraic graph theory, specifically vertex decomposition of graphs. He was particularly proud that he had developed something new, as he was again in 1981 when my sister, Maggie, was born.
In 1986, working for National Semiconductor, Dai was transferred to Germany. Dai and Sally divorced and in 1996 Dai met Marion Heegner. The two were a happy couple, playing music, visiting the Bavarian countryside, and spending time with family and friends. Dai was also a keen bridge player, playing with the same group of people for about 30 years. A voracious reader, he retired in 2014 with his flat in Munich and house in Bad Kohlgrub full of books.
In July 2020, Dai was diagnosed with a brain tumour that proved fatal.
He is survived by Marion, whom he married in 2019, Maggs and me, and Joan and Gareth.
