Mattias Andersson Joachim Gudmundsson Christos Levcopoulos Approximate distance oracles for graphs with dense clusters. 142-154 2007 37 Comput. Geom. 3 http://dx.doi.org/10.1016/j.comgeo.2004.12.011 db/journals/comgeo/comgeo37.html#AnderssonGL07