Walter Hayman

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Second youngest Fellow of the Royal Society, who had links across the Iron Curtain

Professor Walter Hayman, who has died aged 93, was a mathematician best known for his fundamental work on complex analysis and potential theory, and was the second youngest person to be elected a Fellow of the Royal Society during the 20th century; at the time of his death he was the second-longest serving FRS after his lifelong friend Freeman Dyson. In his five seminal textbooks and at least 200 scientific papers he provided solutions to some of the most famous problems in complex functions. These included the so-called asymptotic Bieberbach conjecture, for which he provided a definitive proof in 1955. With his wife Margaret he also founded the British Mathematical Olympiad and together they forged the links across the Iron Curtain that led to the global expansion of the International Mathematical Olympiad, which Margaret continued to run for many years.

Kurt Hayman was born in Cologne on January 6 1926 into an academic family. His father, Franz Haymann (sic), was Professor of Law at the University of Cologne, and his mother Ruth, née Hensel, was the daughter of the mathematician Kurt Hensel and his wife Gertrud Hahn. Gertrud's nephew Kurt Hahn was the educationalist who founded Salem College in Germany (attended by the Duke of Edinburgh) and then, after he was forced to leave Germany by the Nazis, Gordonstoun in Scotland. Ruth's great-grandmother was Fanny Mendelssohn, sister of Felix and a noted composer in her own right. Walter spent happy early years in a comfortable home, surrounded by a large extended family of aunts, uncles and cousins. In an article in the Guardian Walter's daughter Sheila wrote of her father's efforts to recreate the flavours of his German childhood with "raw mince sandwiches instead of steak tartare, and on occasional visits to the countryside, whatever wild mushrooms he could find that looked slightly familiar".

The food, she surmised, was probably the only way he could summon the memory of a childhood that ended "first, at the age of seven in 1933, when he lost an older brother and discovered from the Nazis that he was not, after all, a good little German boy but a Jew. Then, five years later, when he was put on a train by loving parents & and got off on his own in a place where he knew nobody, wasn't allowed to speak his native language, and started every day with a cold shower and a brisk hour of bullying."The place was Gordonstoun, an institution Walter seems to have enjoyed as much as the Prince of Wales did at a later stage. The decision to send the young Prince to the school has been widely attributed to his father, and Hayman took a vicarious revenge on his royal fellow-sufferer's behalf at a Buckingham Palace garden party when he reminded Prince Philip of his youthful role as fag for a cousin of Hayman's at Salem. Through the kindness of a friend of Kurt Hahn's who had invited Walter for his first Christmas in England, he contrived to get his parents out of Germany in April 1939; Walter stayed at Gordonstoun until a major scholarship took him, at the age of 16, to read Mathematics at St John's College, Cambridge.

After graduation he undertook research under Mary (later Dame Mary) Cartwright, but the many forced disruptions of his life had left him longing for stability, so when he was offered a lectureship at King's College, Newcastle in 1947 at only 21 years old, he took the job and married a fellow Cambridge graduate, Margaret Crann, that September.

He became a Reader at the University of Exeter in 1953 and three years later he was elected FRS and appointed as the first Professor of Pure Mathematics at Imperial College, London. There, for the next 32 years, he ran a school in Complex Analysis which attracted mathematicians from all over the world. Margaret forged her own career in maths education, becoming President of the Mathematical Association. They had three daughters with whom they travelled widely, making contacts through the international language of mathematics. Hayman also enjoyed other languages, and took pride in being able to speak at least some words in every country he visited, all of which he delivered with the same strong German accent.

In 1966 they drove to Moscow, with Margaret at the wheel of the family Rover, to attend an International Mathematical Conference at the Atomic Weapons Research Centre just outside the capital. The previous year the Haymans had founded the British Mathematical Olympiad, and the trip to Moscow led to the United Kingdom becoming the first western country to send a team to the International Mathematical Olympiad, until then a preserve of communist states. Hayman served as dean of the Royal College of Science and vice-president of the London Mathematical Society. He received numerous honorary degrees and was elected to the Finnish Academy of Science and Letters, the Bavarian Academy, and the Accademia dei Lincei of Rome. After retiring from Imperial College in 1985 he was appointed to a part-time post as Professor of Pure Mathematics at the University of York, which he held until 1993. In 1995 he returned to Imperial as a Senior Research Fellow, keeping an office to which, until recently, he travelled every week to answer correspondence and play flute sonatas with a colleague. He had met his first wife, Margaret, at a Quaker meeting in Cambridge; before that he had been Jewish (without knowing it), Lutheran in his early childhood, and Anglican at Gordonstoun, where he dutifully took communion with the other boys. On his second marriage he converted to his new wife's religion of Islam, but being unable to join the religion of his third wife, a lapsed Catholic, he reverted to Quakerism and attended Painswick Meeting in Gloucestershire, where he was known, until he moved away at the age of 90, for his dedication to washing the tea and coffee cups.

He explained this ecumenical attitude to religion by saying that the world's great religions were like the faces of a mountain, which grew more alike as they climbed closer to God. But it also spoke of a deep need to belong, which resulted in a vast circle of acquaintance around the world, and a warm-hearted willingness to help anybody who came his way. At the time of his death he was being looked after by the wife of one of these protégés, whom he had befriended through his voluntary work at Bail for Immigration Detainees. Hayman never forgot those who had saved his life in the 1930s. He supported the organisation Freedom from Torture, and dedicated much time after the war to organisations that looked after refugee academics in Britain. At a time when racism was rife and discrimination legal, the Haymans gave a home to visiting scholars from India, Louisiana, China and Japan. Margaret Hayman died in 1994 and the following year he married the mathematician Dr Waficka al-Katifi. She died in 2001 and in 2007 he married, thirdly, Marie Jennings, the former financial regulator and consumer champion, whom he had met after reading her autobiography, Diamonds and Pearls. She died in 2015. Walter Hayman is survived by the three daughters of his first marriage.

Professor Walter Hayman: born January 6 1926, died January 1 2020

30 January 2020 © Telegraph