Alex Groce Daniel Kroening Flavio Lerda Understanding Counterexamples with explain. 453-456 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3114&spage=453 2004 conf/cav/2004 CAV db/conf/cav/cav2004.html#GroceKL04