Patrick Doherty Witold Lukaszewicz Andrzej Szalas Tolerance Spaces and Approximative Representational Structures. 475-489 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2821&spage=475 2003 conf/ki/2003 KI db/conf/ki/ki2003.html#DohertyLS03