A Theory for Simulator

This paper presents a possible formalisation of the notion simulator tool for process languages like ACP, CCS, ()CRL, LOTOS and PSF. First we give precise deenitions for the notions simulator and simulation. Then we can investigate the equivalence that a simulator induces on the explored process terms. This is done by considering two processes, say p and q; equivalent if each simulation of p is also a simulation of q and vice versa. It is proven that there is nòreasonable' simulator inducing bisimulation equivalence. Furthermore it is demonstrated that simulators inducing coarser equivalences, e.g. ready, failure and trace equivalences, are unlikely to be computationally tractable. Our conclusion is that a practical simulator induces an equivalence that is ner (less identifying) than bisimulation and even ner than graph isomor-phism.