Apr.-May 2007      Visiting University of California, Los Angeles

Jan-Mar. 2007        Visiting University of California, Irvine

Fall 2004                Samuel Eilenberg Visiting Professor, Department of Mathematics, Columbia University

Jan-Jun 2002          Gordon Moore Visiting Professor, Department of Mathematics, California Institute of Technology 

Fall 1998                Samuel Eilenberg Visiting Professor, Department of Mathematics, Columbia University

1996                       John Harvard Fellow, Issac Newton Institute for Mathematical Sciences and Faculty of Mathematics, 

                               University of Cambridge,U.K.

1991 - 1992            Special Chair, Department of Mathematics, National Tsing Hua University, Taiwan

1991 - 1992            Wilson T.S.Wang Distinguished Visiting Professor, Department of Mathematics,

                                The Chinese University of Hong Kong

Sept. 1990               Distinguished Visiting Professor,

                                Department of Mathematics, State University of New York, Stony Brook

Fall 1990                 Sherman Fairchild Distinguished Visiting Scholar, Department of Mathematics,
                                California Institute of Technology

Fall 1986                 Sid Richardson Centennial Chair in Mathematics and Visiting Professor,
                                Department of Mathematics, University of Texas at Austin