CB following considerations : 1) trace languages associated 'to marked simple proper nets are recognizable, and therefore their equivalence implies the equivalence of the related sequential languages1 2) the two marked simple proper nets Rl and R2 of fig . 3 are B-equivalent therefore also O-equivalent and 5-equivalent) but are not C5-equivalent therefore neither CO-equivalent nor CB-equivalent).
Nm , where m is the number of root classes of ~. In each disjoint net Nj two or more transitions may occur such that: they derive from the splitting of a communication transition ' Le. ~i their label is x,]. or X,l ]. e. e. they are copies of the same transition x , copies which are necessary for the merging of x with n different transitions in other disjoint nets. Then their multiple occurences are reduced to one and labelled by x the corresponding transitions in all the other subnets are labelled by and all x.