Dirk Draheim Winfried Neun Dima Suliman Classifying Differential Equations on the Web. 104-115 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3119&spage=104 2004 conf/mkm/2004 MKM db/conf/mkm/mkm2004.html#DraheimNS04