Bruno Courcelle David Janin Workshop on Logic, Graph Transformations, Finite and Infinite Structures. 448-450 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3256&spage=448 2004 conf/gg/2004 ICGT db/conf/gg/icgt2004.html#CourcelleJ04