1947 ging er an die Columbia University in New York, wo er bis zu seiner Emeritierung blieb, zweimal Dekan des Fachbereichs war und 1982 „University Professor“ (dort die höchste Position) wurde. ###>==Biography==He was born in Warsaw, Russian Empire (now in Poland) and died in New York City, USA, where he had spent much of his career as a professor at Columbia University.