Revised report: October 2007

**Keywords**:* Concurrency, labelled transition systems,
modal logic, branching bisimulation, divergence, coloured traces.
*

- Preliminary report (June 2006) available as dvi, ps, pdf and tex file. In this version Lemma 5.3, and hence the proof of Corollary 5.4, is incorrect. This mistake has been corrected in October 2007.
- Revised report (October 2007) available as dvi, ps, pdf and tex file.
- A further revision (December 2008), with a slightly different title, obtained by adding didactic background material, is available at http://theory.stanford.edu/~rvg/abstracts.html#67.

rvg@CS.Stanford.EDU