“…As shown by Betz and Helmert (2009), h+ is very informative but unfortunately NP-hard to compute (Bylander, 1994) and also hard to approximate (Betz & Helmert, 2009). As this relaxation does not use information which may be essential for the detection of un-solvability of the original instance (namely the destruction of fluents), a lot of research has been carried out to take some deletes into account (Fox & Long, 2001;Gerevini, Saetti & Serina, 2003;Helmert, 2004;Helmert & Geffner, 2008;Keyder & Geffner, 2008;Cai, Hoffmann & Helmert, 2009). Another recent approach (Haslum, Slaney & Thiébaux, 2012;Keyder, Hoffmann & Haslum, 2012) consists in enriching the classical relaxation with a set of fact conjunctions.…”