Université Paris VI (April - September 1999)
Academia Sinica (July/August 1998, September/October 1997,
December 1996, August 1995, February/March/August 1994, July 1993,
February 1992)
Universität des Saarlandes (November 1995, October/November 1993,
May 1989)
City University of New York (May 1995)
Fujitsu Laboratories Limited (August 1993)
Università degli Studi di Roma "La Sapienza" (March 1990)
University of London (December 1988 - April 1989)
Oxford University (November 1988)
Karl Marx Universität (October 1988)