Amir Pnueli Abstraction for Liveness. 146-146 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3385&spage=146 2005 conf/vmcai/2005 VMCAI db/conf/vmcai/vmcai2005.html#Pnueli05