Hans Leo Bodlaender, Arie M. C. A. Koster. Safe Seperators for Treewidth. In Lars Arge, Giuseppe F. Italiano, Robert Sedgewick, editors, Proceedings of the Sixth Workshop on Algorithm Engineering and Experiments and the First Workshop on Analytic Algorithmics and Combinatorics, New Orleans, LA, USA, January 10, 2004. pages 70-78, SIAM, 2004.