Thomas T. Hildebrandt Henning Niss Martin Olsen Jacob W. Winther 61-80 2006 150 Electr. Notes Theor. Comput. Sci. 1 http://dx.doi.org/10.1016/j.entcs.2005.12.024 db/journals/entcs/entcs150.html#HildebrandtNOW06