Roxana Dietze Manfred Kudlek Olaf Kummer Decidability Problems of a Basic Class of Object Nets. 295-302 2007 79 Fundam. Inform. 3-4 http://iospress.metapress.com/openurl.asp?genre=article&issn=0169-2968&volume=79&issue=3&spage=295 db/journals/fuin/fuin79.html#DietzeKK07