Serge Abiteboul Stephen Alstrup Haim Kaplan Tova Milo Theis Rauhe Compact Labeling Scheme for Ancestor Queries. 1295-1309 2006 35 SIAM J. Comput. 6 http://dx.doi.org/10.1137/S0097539703437211 db/journals/siamcomp/siamcomp35.html#AbiteboulAKMR06