R. Ayyagari, B. Park, D. Hershberger, and H. Kargupta. Data Mining and Knowledge Discovery: Theory, Tools, and Technology, volume 4384 of SPIE Proceedings, page 138-148. SPIE, (2001)
J. Snoeyink, and J. Hershberger. Discrete and Computational Geometry, volume 6 of DIMACS Series in Discrete Mathematics and Theoretical Computer Science, page 309-350. DIMACS/AMS, (1990)