Branching bisimulation for context-free processes

The branching bisimulation defined by Van Glabbeek and Weijland takes care of preserving the branching structure of processes even though silent actions are taken. Branching bisimulation is obviously decidable for finite state processes. A proof that it is also decidable for reduced and proper context-free processes has been given by Huttel. Going further along these lines, we prove that the class of reduced and proper context-free processes is closed under quotient by their greates branching bisimulation. moreover, the construction of the factor graph is in PSPACE