BarannykT. A., BarannykA. F., and YurykI. I. 2017. “Exact Solutions of the Nonliear Equation $u_{tt} = = a(t) uu_{xx} + b(t) u_x^2 + c(t) U $”. Ukrains’kyi Matematychnyi Zhurnal 69 (9), 1180-86. https://umj.imath.kiev.ua/index.php/umj/article/view/1768.