Professor Adjunct, University of Colorado, Boulder, CO, 2008 - current
Distinguished Research Professor, Bowling Green State U., 1993 - 2003
Professor, BGSU, 1971 - 2003
Chair, Dept. of Mathematics, BGSU, 1981 - 1983
Visiting Professor, Simon Fraser U., Vancouver, BC, Canada, 1983 - 1984
Professor, University of Wisconsin, Madison, WI, 1971 - 1972
Associate Professor, UW, 1966 - 1971; Assistant Professor, UW, 1964 - 66
Postdoctoral Fellow, University of Chicago, 1962-1964
NATO Postdoctoral Fellow, University of Tubingen, Germany, 1961-1962