We are greatly saddened by the passing of Donald Kahn, on January 16, 2015. Don was a giant presence in the department, through his contributions in so many ways, his personal engagement with everyone around him, and notably the pleasant hours that so many of us spent talking with him about everything under the sun. Through these connections with him we became aware that he was a rare individual: a Renaissance Man if ever there was one. He was supremely and broadly talented, and not just in technical directions. Prominent among his talents were the ability to reassure, to provide sound, wise and balanced advice, to tell jokes and to entertain us through his love of conversation and of being with others. He was a great person to be around: you knew that if he was present at the lunch table the conversation would never flag. If you told a joke he would come back with 2 or 3 more. He was modest and motivated by the sheer pleasure of doing things, not by competition.
Donald William Kahn was born and grew up in New York City, primarily in Belle Harbor, Queens. According to the anecdotes he told about this time, it was a neighborhood with a rough edge to it which provided a compulsory education in being street-smart. He was born into a family of noted longevity, his father being the investor Irving Kahn who died recently at the age of 109, just a few weeks after Don. His mother, Ruth Perl Kahn, had a Ph.D. in psychology. After attending high school at Woodmere Academy he went to Cornell University as an undergraduate, where he decided to study mathematics. He then received his Ph.D. at Yale University in 1961 under the supervision of William Massey, writing a thesis with the title, 'On the Real Cohomology of Fibre Spaces'. After this he was a Ritt Assistant Professor at Columbia University working with Samuel Eilenberg which, incidentally, provided him with many stories about Eilenberg's no-nonsense approach. Don moved to Minnesota in 1964 where he became assistant professor of mathematics. Shortly after arriving, he spent the following spring and summer visiting the University of Heidelberg in Germany. He was promoted to associate professor in 1967 and full professor in 1984. He served twice as the department's Director of Graduate Studies from 1992 to 1999. Don retired and assumed the rank of Professor Emeritus in 2010. During this time he was the author of 26 research publications and two mathematical books, the first an undergraduate text on topology which came out in 1975 and the second a more advanced treatment on global analysis which appeared in 1980. Both books remain in print. He supervised 8 Ph.D. students at the University of Minnesota.
Don met his wife Phyllis (State Representative Phyllis Kahn) when they were both students at Cornell and she was studying physics. It always seemed that Don was a very appropriate partner for such a prominent and strong politician: his own political sense was highly developed and astute, and he relished the contact with all, including the famous and influential. At gatherings he could invariably be seen using his strong social skills with whomever he met. It always appeared that he knew everyone in the room, and he probably did.
Don was passionate about all of the arts, but the art forms in which he was a most skilled practitioner were music and photography. They both occupied a large part of his time. Don enjoyed music in all its forms and was knowledgeable about it. You could discuss with him at one moment performance details of a classical piano trio, moments later be hearing about the jazz greats that he heard in New York in the 1950s and early 60s (he had heard them all) and after that be learning from him about songs from Broadway musicals. He was talented as a performer, on keyboards (piano and harpsichord), cello and trombone. He played classical chamber music regularly and played in an amateur chamber orchestra on Wednesdays. He went to hear jazz often and worked on jazz performance at the piano via transcriptions. He admired particularly the compositions of Thelonius Monk and could perform Round Midnight, as well as other pieces, at a moment's notice.
Don spent a great deal of time on photography. At departmental events he would invariably be there with his Leica, and the same was true everywhere he went where there was the opportunity to take photos. Often he shot black and white, and he would develop the prints himself, so that carefully cropped enlargements would appear on the mail room bulletin board a day or two after a mathematical event. We were lucky to have such a source of high-quality photos. For many years he would also take color slides and use the Cibachrome process to make prints from them at home, something only the serious enthusiast would be likely to do. When digital methods became available he was at first lukewarm about the idea, but more recently he took slides which he would scan and print out in color with a digital printer. Whether produced digitally or with chemicals, Don would always have on display in his office several large boards of 10 by 8 color enlargements of places he had been. Rather recently Don mounted an exhibition of photos taken in China. Just last year he published a book he had written with the title, 'Photography: a concise history'.
We remember Don's natural ability with languages. His command of French and German were extraordinary, and were strengthened during his visits to Toulouse and Heidelberg. Apparently he picked up Spanish during a month-long visit to Mexico City, and at the end of the month he gave his last two lectures in the language. It was important to him to use these languages, so that when French-speaking visitors would arrive in the department, for instance, he would speak to them in French. For a while he was attending regular conversation evenings organized by the Alliance Francaise, because he relished doing it.
All of these are remarkable achievements, and on a daily basis he was doing something that was notable. At the time he was Director of Graduate Studies he would take groups of students to the Guthrie to see what was currently playing. If you found the discussion turning to classic movies you would find that he knew in detail, and had an appreciation of, just about everything. We remember in particular his admiration for the cinematic work of Jacques Tati as M. Hulot, and his mild disappointment that times have changed so much that younger generations do not even know of this master, let alone appreciate his humor. At times in his life he was an enthusiastic scuba diver and a chaser of solar eclipses. He also maintained a generously decorated office door!
One area in which Don took the lead was in making donations and in organizing funds to which others could donate. He saw the need to do this with the IMA, and in 2009 he singlehandedly started the Eugene Fabes Directorship Fund, the intention of which was to pay for part of the IMA director's salary. He was prescient in seeing the need for independent endowment funds so as to lessen the reliance on other forms of funding. He set up the Ruth Kahn School of Mathematics Fellowship Fund, a fund which supports graduate students. He was a generous contributor to many other Math funds.
Although he had such a wide range of interests, we must mention that Don's contribution to the mathematical life of the department was never overshadowed by his other activities. Don was a fine and amiable teacher at all levels and a tireless supporter of mathematical research. He was a regular speaker in seminars. He put in considerable effort preparing accounts either of his own research or of expository material for the benefit of others, especially the students, and this meant a lot to him. He saw the importance of attending and supporting seminars on many topics, not just in his own specialty, because he perceived that the life of the department would be made better by this.
In all, we have lost a wonderfully talented colleague who lived life to the full, and who was more than willing to share his experiences with the rest of us. His passing is a great loss.