Grit Denker Carolyn L. Talcott Grigore Rosu Mark van den Brand Steven Eker Traian-Florin Serbanuta 233-247 2007 176 Electr. Notes Theor. Comput. Sci. 4 http://dx.doi.org/10.1016/j.entcs.2007.06.018 db/journals/entcs/entcs176.html#DenkerTRBES07