1973-1976 New York University, Courant Institute of Mathematical Sciences,Instructor
1976-77 University of California, Los Angeles, Assistant Professor
1977-78 University of California, Los Angeles, Associate Professor
1978, FallUniversity of California, Los Angeles, Professor
1979 Jan.–Sept. 1984University of California, Berkeley, Professor
1984 to Sept. 1995 Princeton University, Professor
1994, September New York University Samuel Morse Professor of Arts & Sciences at Courant Institute of Mathematical Sciences
