Nieves R. Brisaboa Susana Ladra Gonzalo Navarro k2-Trees for Compact Web Graph Representation. 18-30 2009 SPIRE http://dx.doi.org/10.1007/978-3-642-03784-9_3 conf/spire/2009 db/conf/spire/spire2009.html#BrisaboaLN09