Wm Randolph Franklin and Varol Akman. Shortest paths in 3-space, Voronoi diagrams with barriers, and related complexity and algebraic issues. In L. Basañez, Gabriel A. Ferraté, and George N. Saridis, editors, Robot Control (SYROCO '85): Proceedings of the 1st IFAC Symposium, volume 1, pages 271–275. International Federation of Automatic Control, Barcelona, Spain, 6–8 November 1985.
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