Stieltjes Memorial Lecture, Dutch Mathematical Society, 1994
British Mathematical Colloquium, 1994
AAAS Lecture at MAA 75th Anniversary Meeting, 1990
Wisconsin Sectional Meeting of MAA, 1988
Illinois Sectional Meeting of MAA, 1987
Joint MAA and AMS meeting, 1985
Mathematical Association of America, 1984
International Congress of Mathematicians, 1983
Canadian Mathematical Society, 1981
Pi Mu Epsilon (J. Sutherland Frame Lecture), 1980
Ontario Mathematical Society, 1977
Society for Industrial and Applied Mathematics, 1969
American Mathematical Society, 1966