Bischi, Gian-Italo, Laura Gardini, and Christian Mira. 1999. “Unbounded Not Diverging Trajectories in Maps With a Vanishing Denominator”. Annales Mathematicae Silesianae 13 (September):91-102. https://trrest.vot.pl/ojsus/index.php/AMSIL/article/view/14140.