Solitar was born September 5, 1932, in Brooklyn, New York. At an early age he showed considerable mathematical gifts. Upon entering Boys High School he joined its mathematics team, which won the championship, in competition with other teams in Brooklyn, three years in a row. Abe Karrass, who was to become Donald's lifetime friend and collaborator, was captain of the team.
Following high school Donald entered Brooklyn College, graduating in 1953 with a B. Sc. While at Brooklyn College he renewed his friendship with Abe Karrass, who acted as his mathematics teacher, essentially replacing all his other teachers. Donald entered the Graduate Program at Princeton, hoping to study group theory under Emil Artin. Artin, however, had by then turned his attention to class field theory. So Donald got an M. Sc. in Mathematics from Princeton, then moved to New York University, where he got his Ph.D. (in 1958) in Group Theory under Wilhelm Magnus. He joined the Mathematics department at Adelphi University in 1959, where Abe Karrass was soon to join him. It was the start of a very close mathematical collaboration, and the continuation of a very close friendship, which lasted fifty years. It 1967 Solitar moved to the Polytechnic University of New York as Professor of Mathematics.
Solitar came to York in 1968 to head the Mathematics department. He was also Acting Chair of the Computer Science department during 1968-73. Through his efforts and those of Karrass, York's mathematics department soon became a world centre in combinatorial group theory. In the winter of 1976, in Toronto, Donald met J. Francien Hageman, who was born in Amsterdam, They married a year later.
Professor Solitar was a "lateral thinker", very often coming up with an unexpected viewpoint. He was well known in the international mathematical community, in particular for the now classic book Combinatorial Group Theory, written jointly (in 1966) with his adviser Wilhelm Magnus and with Abe Karrass. The book was subsequently translated into Russian. In 1982 he was elected Fellow of the Royal Society of Canada. Donald was an inspiring teacher, and in 1985 received an OCUFA Teaching Award.
He had an ebullient and in other ways extraordinary personality, and was extremely generous to all he came in contact with. He is survived by his wife Francien, his sister Miriam, and a large extended family, of which he was the patriarch.
Bob Burns, Israel Kleiner, Alfred Pietrowski
Canadian Mathematical Society