Cost allocation for steiner trees

A se t of points, called consumers, and another point called central supplier, are located i n a Euclidean plane. The cost of constructing a connection between two points i s proportional t o the distance between them. The minimum cost required for connecting a l l the consumers t o the supplier i s given by a minimal Steiner tree. An example i s given i n which for every allocation of the total cost of the tree t o the consumers, a coalition of consumers exists , which i s charged more than the cost required for connecting i t s members t o the central supplier.