1993 with W. Pulleyblank
1995 with A.M.H. Gerards
2007 with Sylvia Boyd
2008 with B. Cook and F. Eisenbrand
2009 with Adrian Vetta
2010 with Mohit Singh and Adrian Vetta
2011 with Mohit Singh and Adrian Vetta
2013 with Fritz Eisenbrand and Adrian Vetta
Graphs and Matroids Cluster, ISMP Atlanta, 2000 Program Committees: CO 1996; ESA 1999; SODA 2002; IPCO 2005; SODA 2005; SIAM Discrete 2008; INOC 2008, APPROX 2009, IPCO 2010 (chair), Canadam 2011, SODA 2013, INOC 2013.