Matthias Baaz Alexander Leitsch CERES in Many-Valued Logics. 1-20 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3452&spage=1 2004 conf/lpar/2004 LPAR db/conf/lpar/lpar2004.html#BaazL04