Bernd Baumgarten Heinz Jürgen Burkhardt Peter Ochsenschläger Rainer Prinoth The signing of a contract - a tree-structured application. 1-18 1985 conf/apn/1985 Applications and Theory in Petri Nets db/conf/apn/apn1985.html#BaumgartenBOP85 http://dx.doi.org/10.1007/BFb0016203