Hans Zantema Alfons Geser A Complete Characterization of Termination of O<sup>p</sup> 1<sup>q</sup> -> 1<sup>r</sup> O<sup>s</sup>. 41-55 1995 conf/rta/1995 RTA db/conf/rta/rta95.html#ZantemaG95 http://dx.doi.org/10.1007/3-540-59200-8_46