1. L.Aceto, On Relating Concurrency and Nondeterminism, Technical Report SI/RR-89/06, University of Sussex, 1989.
2. L.Aceto, D.Murphy, Timing and Causality in Process Algebra, Technical Report 9/93, University of Sussex, 1993, to appear in Acta Informatica.
3. S.Arun-Kumar and M.Hennessy, An Efficiency Preorder for Processes, Acta Informatica 29, pp. 737–760, 1992.
4. G.Boudol, I.Castellani, M.Hennessy, A.Kiehn, A Theory of Processes with Localities, Formal Aspects of Computing 6, pp. 165–200, 1993.
5. F.Corradini, R.Gorrieri and M.Roccetti, Performance Preorder and Competitive equivalence, Tech.Rep. LFCS-95-1, University of Bologna, January 1995.