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MR1791201 (2001g:90029) Bandelt, Hans-Jürgen; Chepoi, Victor; Karzanov, Alexander A characterization of minimizable metrics in the multifacility location problem. Discrete metric spaces (Marseille, 1998). European J. Combin. 21 (2000), no. 6, 715--725. (Reviewer: Sandra L. Arlinghaus) 90B80 (05C12)