Giuliano Armano Giancarlo Cherchi Eloisa Vargiu Planning by Abstraction Using HW[]. 349-361 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2829&spage=349 2003 conf/aiia/2003 AI*IA db/conf/aiia/aiia2003.html#ArmanoCV03