Modifications of Expansion Trees for Weak Bisimulation in BPA

Abstract

The purpose of this work is to examine the decidability problem of weak bisimilarity for BPA-processes. It has been known that strong bisimilarity, which may be considered a special case of weak bisimilarity, where the internal (silent) action $\tau$ is treated equally to observable actions, is decidable for BPA-processes (\cite{BBK,BCS,CHS}). For strong bisimilarity, these processes are finitely branching and so for two non-bisimilar processes there exists a level $n$ that distinguishes the two processes. Additionally, from the decidability of whether two processes are equivalent at a given level $n$, semidecidability of strong non-bisimilarity directly follows. There are two closely related approaches to semidecidability of strong equivalence: construction of a (finite) bisimulation or expansion tree and construction of a finite Caucal base. We have attempted to find out if any of the above mentioned approaches could be generalized to (semi)decide weak bisimilarity.