The notion of bisimilarity, as defined by Park and Milner, has turned out to be one of the most fundamental notions of operational equivalences in the field of process algebras. Not only does it induce a congruence (largest bisimulation) in CCS which have nice equational properties, it has also proven itself applicable for numerous models of parallel computation and settings such as Petri Nets ...

We consider the bisimulation on the transition graphs of pushdown automata. First we give a characterization of bisimulation using the unfolded trees. We recall that the bisimulation is decidable for the subclass of preex transition graphs of context-free grammars. Furthermore any pushdown transition graph is a regular graph: it can be generated by iterated parallel rewritings of a deterministi...