Yuri Matiyasevich Géraud Sénizergues Decision problems for semi-Thue systems with a few rules. 145-169 2005 330 Theor. Comput. Sci. 1 http://dx.doi.org/10.1016/j.tcs.2004.09.016 db/journals/tcs/tcs330.html#MatiyasevichS05