Minimum networks for four points in space
The Steiner tree problem in space is much harder then in the plane. It is shown here, for instance, that Steiner trees on 4 points in space in general cannot be solved by radicals (see also \textit{St. Mehlhos} [Beitr. Algebra Geom. 41, 151-158 (2000; Zbl 0947.90094)]). The optimal Steiner tree ratio for 4 points in space is also determined.
scientific article; zbMATH DE number 1845447