Renate Klempien-Hinrichs Hans-Jörg Kreowski Sabine Kuske Typing of Graph Transformation Units. 112-127 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3256&spage=112 2004 conf/gg/2004 ICGT db/conf/gg/icgt2004.html#Klempien-HinrichsKK04