H. Boucheneb, and G. Berthelot. Theory and Practice of Timed Systems @ ETAPS, volume 65 of Electronic Notes in Theoretical Computer Science, page 1-15. Elsevier, (2002)
G. Berthelot, C. Johnen, and L. Petrucci. CAV (DIMACS/AMS volume), volume 3 of DIMACS Series in Discrete Mathematics and Theoretical Computer Science, page 43-56. DIMACS/AMS, (1990)