Research leaves: 1976-77, 1980-81, 1984 fall, 1988 fall, 1993 fall, Brandeis University (USA); 1998 spring, Northeastern University (USA); 1998 fall, Bielefeld (Germany); 2002 spring, Paderborn (Germany), Bielefeld and Northeastern University; 2005 fall, Bahia Blanca (Argentina) and Paderborn; 2008 spring, Oxford, Bielefeld, Boston, Lincoln (USA); 2010 fall, Bielefeld.
Visits for at least one month: 1997, 1998 Mexico City; 1984 Stuttgart; 1985, 1993 Bielefeld; 1986 Liverpool; 1987 Beijing; 1990 Sao Paulo; 1990, 1991 Paderborn; 1992 Warwick; 1994 Tianjin; 1995 Chemnitz; 1998 Bahia Blanca and Sherbrooke; 2001 SHS, Oslo; 2003, 2004 Mittag-Leffler; 2003 MSRI; 2006, 2007, 2008, 2009, 2010 Bielefeld; 2005 Bahia Blanca; 2008 Oxford.
Shorter visits: Australia, Belgium, Canada, China, Denmark, England, Finland, France, Germany, Greece, Iceland, Holland, India, Iran, Italy, Japan, Mexico, Norway, Poland, Romania, Russia, Scotland, Spain, Sweden, USA.
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