Embedding metrics into ultrametrics and graphs into spanning trees with constant average distortion.

Ittai Abraham Yair Bartal Ofer Neiman Embedding metrics into ultrametrics and graphs into spanning trees with constant average distortion. 502-511 2007 conf/soda/2007 SODA http://doi.acm.org/10.1145/1283383.1283437 db/conf/soda/soda2007.html#AbrahamBN07