Vadim Bulitko Nathan R. Sturtevant Jieshan Lu Timothy Yau Graph Abstraction in Real-time Heuristic Search. 51-100 2007 30 J. Artif. Intell. Res. (JAIR) http://www.jair.org/papers/paper2293.html db/journals/jair/jair30.html#BulitkoSLY07