Shmuel Sagiv On the Expressive Power of Canonical Abstraction. 58 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2937&spage=58 2004 conf/vmcai/2004 VMCAI db/conf/vmcai/vmcai2004.html#Sagiv04