Between 1966 and 2008 he was repeatedly visiting professor at various North American universities, including Dartmouth College (1978), Cornell (1981), University of Kansas, Lawrence (1984), University of Michigan, Ann Arbor (1987), University of Budapest (1990), Washington University, St. Louis (1993), Graz (1994), (1998), (2003), (2007); University of Ohio, Columbus (2008).