1. M. Brazil, J.H. Rubinstein, D.A. Thomas, J.F. Weng and N.C. Wormald, Shortest Networks on Spheres, Proceedings of the DIMACS Workshop on Network Design, to appear.
2. J. Cheeger and D.G. Ebin, Comparison theorems in Riemannian geometry, ( North-Holland Publishing Co., Amsterdam, 1975 ).
3. E.J. Cockayne, On Fermat’s problem on the surface of a sphere, Math. Magazine, Vol. 45 (1972), pp. 216–219.
4. J. Dolan, R. Weiss and J. MacGregor Smith, Minimal length tree networks on the unit sphere, Annals of Oper. Res., Vol. 33 (1991), pp. 503–535.
5. D.Z. Du and F.K. Hwang, A proof of the Gilbert-Pollak Conjecture on the Steiner ratio, Algorithmica, Vol. 7 (1992), pp. 121–135.