Pankaj K. Agarwal, Sergey Bereg, Ovidiu Daescu, Haim Kaplan, Simeon C. Ntafos, Binhai Zhu. Guarding a terrain by two watchtowers. In Joseph S. B. Mitchell, Günter Rote, editors, Proceedings of the 21st ACM Symposium on Computational Geometry, Pisa, Italy, June 6-8, 2005. pages 346-355, ACM, 2005. [doi]
Abstract is missing.