D. Bryant, and M. Steel. Proceedings of the Tenth Annual ACM-SIAM Symposium on Discrete Algorithms (Baltimore, MD, 1999), page 147--155. New York, ACM, (1999)
D. Bryant, J. Tsang, P. Kearney, and M. Li. Proceedings of the Eleventh Annual ACM-SIAM Symposium on Discrete Algorithms (San Francisco, CA, 2000), page 285--286. New York, ACM, (2000)