Regular positions held

• Texas A&M University
  • Regents Professor, 2014–2024.
  • Presidential Professor for Teaching Excellence, 2012–2024.
  • Professor of Mathematics, 1992–2024.
  • Associate Professor of Mathematics, 1987–1992.
  • Assistant Professor of Mathematics, 1984–1987.
• Columbia University
  • J. F. Ritt Assistant Professor of Mathematics, 1980–1984.

Visiting positions held

• Mathematical Sciences Research Institute, Berkeley
  • Member, spring 1996.
• University of North Carolina at Chapel Hill
  • Visiting Associate Professor of Mathematics, 1989–1990.
  • Visiting Lecturer, 1979–1980.