Types and Tokens for Logic with Diagrams.

Frithjof Dau Types and Tokens for Logic with Diagrams. 62-93 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3127&spage=62 2004 conf/iccs/2004 ICCS db/conf/iccs/iccs2004.html#Dau04