Derfel’G. A., RomanenkoY. Y., and SharkovskyO. M. “Asymptotic Discontinuity of Smooth Solutions of Nonlinear $q$-Difference Equations”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 52, no. 12, Dec. 2000, pp. 1615-29, https://umj.imath.kiev.ua/index.php/umj/article/view/4566.