Eithan Ephrati Martha E. Pollack Marina Milshtein A Cost-Directed Planner: Preliminary Report. 1223-1228 1996 conf/aaai/1996-2 AAAI/IAAI, Vol. 2 db/conf/aaai/aaai96-2.html#EphratiPM96 http://www.aaai.org/Library/AAAI/1996/aaai96-181.php