Obituary: Donald Kahn pictured the world through mathematics

With Donald Kahn, a quick question about math often inspired an hourlong conversation about something else entirely.

Music. French politics. Photography.

During his decades at the University of Minnesota, the mathematics professor became as known for these broad discussions as his specific study of topology. One student went to Kahn to prepare for an exam and approached Jonathan Rogness, an assistant professor, afterward. "He said, 'Don is great, but tell me — how do you get him to talk about mathematics?' "

Kahn, a photographer, storyteller and husband of 58 years to state Rep. Phyllis Kahn, died Jan. 16. He was 79.

Kahn was born in New York City, where his father, Irving Kahn, who is now 109 years old, became a legendary investor. His mother, Ruth, had a Ph.D. in psychology, Phyllis Kahn said, so it was no surprise that Don's baby book included the results of a Rorschach test.

"Brilliant and sensitive," it said. "No fears, no feeling of inferiority. Has accepted birth without trauma and places himself squarely in this world."

Upon receiving his first box camera as a birthday present in 1942, "I immediately shot pictures of fighter aircraft in the sky," he later wrote. "I was devastated to see that the planes came out as tiny dots." Years later, "I got my first Leica and began to learn what this is all about."

"He always took the extra step to say, How do we make this interesting?" said Jeremy Kahn, 50, of Montreal.

Kahn and Phyllis met as students at Cornell University, where Don roomed with three men, Phyllis said. "I dated each of them sequentially, and Don was the last."

After earning his Ph.D. at Yale University in 1961, Kahn taught at Columbia University and then in Heidelberg, Germany. He spoke German and French fluently and had "an incredible ability" to pick up languages, Phyllis Kahn said. Despite not knowing Spanish at the start of a monthlong teaching stint in Mexico City, he gave his last two lectures in the language.

Kahn came to the U in 1964, recruited because of "his very strong work in topology," said Prof. Peter Olver, head of the School of Mathematics. His 1975 textbook was "a short but elegant introduction to the subject," said Rogness, who read it before becoming one of Kahn's Ph.D. students.

Kahn twice served as the department's director of graduate studies and, even after retiring in 2010, continued grading preliminary exams and working with students. "It was well-known how generous he was with his time," Rogness said. He'd tell detailed, funny stories about past colleagues and snapped portraits at events.

"He was the more responsible person, the more attentive person in this marriage," Phyllis Kahn said. "The one who probably did more than he was supposed to."

Though he spent many hours developing photographs in his darkroom, some were surprised when, in 2014, he published a "concise history" of photography. People thought it was "so contradictory that he was both a mathematician and a musician and photographer," Jeremy Kahn said. But his father's brand of math was theoretical, almost artful, he said.

Kahn was interested "not only in the pictorial aspect of what the image was, but in thinking about photography as a medium of information or exchange of ideas," said Tom Rose, a professor in the Department of Art. Kahn had hoped to travel with Rose to Beijing, where Rose had established a program based on exchanging photographs.

But after breaking his leg last year, Kahn encountered other health problems.

Passionate about global and local politics, Kahn occasionally wrote letters to the editor about Nicaragua, Vietnam and other countries, at least once using math to prove his point. He was active in his wife's many campaigns, organizing the effort to put door-hangers across the district when she ran for the state House of Representatives for the first time in 1972.

"But they would always express positives."

Other survivors include brothers Alan and Thomas Kahn, daughter Tamar McNally and six grandchildren. Private services have been held.