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graph Trevor Fenner S hool of Computer S ien e Birkbe k College, University of London Malet Street, London WC1E 7HX email trevor d s.bbk.a .uk Abraham Flaxman Department of Mathemati al S ien es Carnegie Mellon University Pittsburgh, PA, 15213, USA email abie mu.edu Alan Frieze y Department of Mathemati al S ien es Carnegie Mellon University Pittsburgh, PA, 15213, USA email alan random.math. mu.edu Mar h 17, 2003