“…Bergstra and Klop showed in Reference [19] that a finite ground-complete axiomatisation modulo bisimilarity can be obtained by enriching CCS with two auxiliary operators, namely, the left merge and the communication merge |, expressing, respectively, one step in the asymmetric pure interleaving and the synchronous behaviour of . Their result was then strengthened by Aceto et al in Reference [10], where it is proved that, over the fragment of CCS without recursion, restriction, and relabelling, the auxiliary operators and | allow for finitely axiomatising modulo bisimilarity also when CCS terms with variables are considered. Moreover, in Reference [14], that result is extended to the fragment of CCS with relabelling and restriction, but without communication.…”