Samoilenko, V. G., and Y. I. Samoilenko. “Asymptotic Two-Phase Solitonlike Solutions of the Singularly Perturbed Korteweg-De Vries Equation With Variable Coefficients”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 60, no. 3, Mar. 2008, pp. 388–397, https://umj.imath.kiev.ua/index.php/umj/article/view/3162.