Ludwik Czaja An Axiomatic Framework for Proving Correctness of Nets. 45-64 2005 67 Fundam. Inform. 1-3 http://iospress.metapress.com/openurl.asp?genre=article&issn=0169-2968&volume=67&issue=1&spage=45 db/journals/fuin/fuin67.html#Czaja05