Vervolgens was hij tot 1971 hoogleraar aan de Stanford-universiteit en tot 1992 "Graduate Research Professor" en directeur van het "Centre for Mathematical System Theory" aan de Universiteit van Florida. ###>He was a professor at Stanford University from 1964 until 1971, and then a Graduate Research Professor and the Director of the Center for Mathematical System Theory, at the University of Florida from 1971 until 1992.