Massimo Bartoletti Pierpaolo Degano Gian Luigi Ferrari Roberto Zunino Hard Life with Weak Binders. 49-72 2009 242 Electr. Notes Theor. Comput. Sci. 1 http://dx.doi.org/10.1016/j.entcs.2009.06.013 db/journals/entcs/entcs242.html#BartolettiDFZ09