1. Bozkaya B, Tansel B (1998) A spanning tree approach to the absolute p-center problem. Locat Sci 6:83–107
2. Chen ML, Francis RL, Lowe TJ (1988) The 1-center problem: exploiting block structure. Transp Sci 22:259–269
3. Christofides N (1975) Graph theory: an algorithmic approach. Academic, New York
4. Christofides N, Viola P (1971) The optimum location of multi-centers on a graph. Oper Res Quart 22:145–154
5. Dantzig GB (1967) All shortest routes in a graph. Theory of Graphs, International Symposium, Rome, 1966, Gordon and Breach, New York, pp 91–92