Christian Dimitrovici Udo Hummert Laure Petrucci Semantics, composition and net properties of algebraic high-level nets. 93-117 1990 conf/apn/1990 Applications and Theory of Petri Nets db/conf/apn/apn1990.html#DimitroviciHP90 http://dx.doi.org/10.1007/BFb0019971