A talented mathematician, Mary Warner supported her diplomat husband in all his postings overseas while pursuing her own career and bringing up three children, two of whom died tragically before their own considerable talents had matured.

Shortly after her marriage to Gerald Warner, he was posted to China. There, she embarked on joint research with a professor at Beijing University, but this came to an untimely end when he came to their flat one day, crouched beside the sofa to avoid any eavesdropping microphones, and told her that, although he was a liberal, the beginning of Chairman Mao's Great Leap Forward meant that he could see her no longer.

In Rangoon, her husband's next posting, she launched and taught the first postgraduate course in higher mathematics, and in Warsaw, where they went after Rangoon, she took a doctorate in topology, which had been developed by Polish mathematicians in the 1930s. Only afterwards was she told that all candidates for higher degrees had also to pass an oral exam in Marxist-Leninist theory. Somehow the University of Warsaw managed to overlook the requirement.

Back in London in 1968, she lectured at the City University for six years until her husband was posted to Kuala Lumpur, where she became the only person to hold teaching appointments in both the Malaysian and the Chinese universities. In 1976 she returned to City University as a reader in mathematics, becoming a professor in 1991.

Mary Wynne Davies went to school in Wales, where her father was headmaster of a grammar school, and then won a scholarship to Somerville College, Oxford, where she was disappointed not to take a first. But she stayed on as a graduate research student under Professor Henry Whitehead, the eminent topologist. This is a branch of mathematics so abstruse that even she had great difficulty explaining what she was up to to her friends. "You mustn't think that I can do sums," she would say, "because I can't." Within this discipline she specialised, first in algebraic topology, and then, as so-called fuzzy logic attracted increasing attention, in its analogue: fuzzy topology. At City University she was known as a particularly sympathetic teacher, and several of her foreign research students tried to entice her to spend time at their own universities as a visiting professor. She was also a loyal friend. She once went to visit a male colleague a good 15 years older than herself when he was seriously ill in hospital. Visiting was restricted, and she was asked what relation she was to the patient. "I'm his mother," she replied.

Despite her travels, Mary Warner never lost her Welshness. She was always direct, saying what she thought with a caustic wit, though in order to spare her husband professional embarrassment she did her best to keep her strong emotions under control.

Once when they were giving a diplomatic dinner party in a Geneva restaurant noted for its tartes a la creme , a guest was mocking Welsh poetry, of which Mary Warner was very fond. Becoming more and more indignant, but prevented from fighting back, she finally turned illogically but effectively on her husband, throwing at him one of the specialities of the house and bringing the conversation to a full stop.

Mary Warner is survived by her husband, now Sir Gerald Warner, and by one daughter.

© The Times, 1998