S. Mueller, B. Kruck, and P. Baudisch. Proceedings of the SIGCHI Conference on Human Factors in Computing Systems, page 2585--2592. New York, NY, USA, ACM, (2013)
D. Cohen-Steiner, H. Edelsbrunner, and D. Morozov. Proceedings of the Twenty-second Annual Symposium on Computational Geometry, page 119--126. New York, NY, USA, ACM, (2006)