Christian Stahl Peter Massuthe Jan Bretschneider Deciding Substitutability of Services with Operating Guidelines. 172-191 2009 2 T. Petri Nets and Other Models of Concurrency http://dx.doi.org/10.1007/978-3-642-00899-3_10 journals/topnoc/2009-2 db/journals/topnoc/topnoc2.html#StahlMB09