## Approximating Weak Bisimilarity of Basic Parallel Processes

This paper explores the well known approximantion approach to decide weak bisimilarity of Basic Parallel Processes by refinement. We look into how different refinement functions can be used to prove weak bisimilarity decidable for certain subclasses and also show their limitations for the general case. In particular, we show a lower bound of \(\omega*\omega\) for the approximants which allow weak steps and a lower bound of \(\omega+\omega\) for the approximants that allow sequences of actions.