Flemming Nielson Hanne Riis Nielson Helmut Seidl Normalizable Horn Clauses, Strongly Recognizable Relations, and Spi. 20-35 2002 conf/sas/2002 SAS http://link.springer.de/link/service/series/0558/bibs/2477/24770020.htm db/conf/sas/sas2002.html#NielsonNS02