Closed and Logical Relations for Over- and Under-Approximation of Powersets.

David A. Schmidt Closed and Logical Relations for Over- and Under-Approximation of Powersets. 22-37 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3148&spage=22 2004 conf/sas/2004 SAS db/conf/sas/sas2004.html#Schmidt04