Ludwik Czaja Proving Nets Correct via Cause-Effect Structures (An Experiment). 165-183 2003 54 Fundam. Inform. 2-3 http://iospress.metapress.com/openurl.asp?genre=article&issn=0169-2968&volume=54&issue=2&spage=165 db/journals/fuin/fuin54.html#Czaja03