Barannyk, T. A., A. F. Barannyk, and I. I. Yuryk. “Exact Solutions of the Nonliear Equation $u_{tt} = = a(t) uu_{xx} + b(t) u_x^2 + c(t) U $”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 69, no. 9, Sept. 2017, pp. 1180-6, https://umj.imath.kiev.ua/index.php/umj/article/view/1768.