Francesco Bernardini Robert Brijder Grzegorz Rozenberg Claudio Zandron Multiset-Based Self-Assembly of Graphs. 49-75 2007 75 Fundam. Inform. 1-4 http://iospress.metapress.com/openurl.asp?genre=article&issn=0169-2968&volume=75&issue=4&spage=49 db/journals/fuin/fuin75.html#BernardiniBRZ07