Complex sentence: In 1981/82 and from 1989 to 1992 he was visiting professor at the Max Planck Institute for Mathematics in Bonn and a guest researcher at places including Paris, Princeton, Berkeley, Chicago, Aarhus, St. Petersburg, Moscow and Beijing.
Split into simpler sentences: In 1981/82 and from 1989 to 1992 he was visiting professor at the Max Planck Institute for Mathematics in Bonn. He was also a guest researcher at places including Paris, Princeton, Berkeley, Chicago, Aarhus, St. Petersburg, Moscow and Beijing.