While on sabbattical from CUNY, I held a Visiting Professor position at the Universiteit van Amsterdam at the Institute for Logic, Language and Computation during April–August 2007. During the two years previous to this, I was an NWO-sponsored Bezoekersbeurs Visiting Researcher there, during June–August 2005 and June 2006.  While in Amsterdam, I worked with Benedikt Löwe, particularly on our work concerning the modal logic of forcing.

I held a Mercator Gastprofessor position from the DFG at Universität Münster, Institut für mathematische Logik, during May to August, 2004.

I held the position of Associate Professor at Georgia State University in the Department of Mathematics and Statistics during the 2002 – 2003 academic year.

During the 2000 – 2001 academic year, I held the position of Visiting Associate Professor of Mathematics at Carnegie Mellon University.