JANOS PACH is Professor of Computer Science at City College of New York and Senior Research Fellow at the Mathematical Institute of the Hungarian Academy of Sciences. He received his PhD in mathematics from Eotvos University, Budapest, in 1980 and has had visiting positions at various universities, including the University College of London, McGill University, the Courant Institute of New York University, and Tel Aviv University. He serves on the editorial boards of three mathematical and computer science journals and has been an invited speaker at many conferences. He has published more than one hundred research papers, mostly in discrete and computational geometry and in combinatorics. He received the Lester R. Ford Award in 1990 and the Renyi Prize in 1993. PANKAJ K. AGARWAL is Associate Professor in the Computer Science Department of Duke University. He received his PhD in computer science from the Courant Institute of Mathematical Sciences, New York University, in 1989. He is the author of Intersection and Decomposition Algorithms for Planar Arrangements, and a coauthor of Davenport-Schinzel Sequences and Their Geometric Applications. He has published several research papers and has given talks at many conferences. He was awarded the National Young Investigator Award in 1992.